Could your best friend be sleeping with your husband? It's more common than that you think, warns TRACEY COX. These are all the warning signs

Being cheated on is agony.But your much-loved partner cheating on you with the woman who held your hair back at your hen do, your mother loves and who you’ve told everything to for the last 30 years, is a special kind of hell. You lose your partner and the person you’d call for help in a heartbeat.Yet it happens far more often than you’d like to think.Cheating flourishes where there’s opportunity, familiarity and trust. A close friend ticks all three boxes: she’s in your home, she’s comfortable with your husband and you don’t think twice about leaving them in the same room.I’m not telling you to scrutinise every friendship – please don’t! Most close friends are exactly who they appear to be – and you’ll end up with no friends at all if you make yourself paranoid.But if your gut tells you something isn’t right, here are some signs you could be right. Cheating flourishes where there’s opportunity, familiarity and trust. If your gut tells you something isn’t right, here are some signs you could be right...GIVEAWAY BODY LANGUAGEOur bodies tell the truth even when we don’t.But a word of warning with this one: you need to apply a HUGE dollop of common sense to all body language cues. Someone crossing their arms can mean they’re uncomfortable, but it can also mean they’re simply cold.Your husband and friend are suddenly weirdly formal. You’d expect the opposite: for them to be all over each other. But guilty people often do the opposite. If your friend used to tease your partner and joke around with him but now seems to ignore him, ask yourself what’s changed. Sudden formality between previously relaxed people is a classic tell.They never look at each other – but glance over often. People having an affair tend to avoid eye contact: they’re worried their feelings will be apparent if they do. (They aren’t wrong: our eyes soften when we look at someone we love). If they’re avoiding each other’s eyes, watch for constant, fast check-ins. They’ll dart quick looks at each other when they think they can get away with it. If they do happen to lock eyes, they get ‘sticky’ - neither is able to look away immediately.Their bodies angle towards each other. Torsos, feet and knees point at the person we’re drawn to. Watch them in a group: if your friend’s entire body points towards your partner and his does to her, it could be an unconscious sign of attraction.The ‘accidental’ touch. Plenty of people have been caught when someone takes a photo they don’t know is happening. It reveals his hand on her bottom as they walk through a doorway. Her hand on his as she squeezes past him in the kitchen. Again, one touch can mean nothing but affection but a pattern – or a touch in a sexual zone - is worth noting.Pulling away from each other too quickly. 'My friend Amanda had just had a termination,' Nicole, 37, told me. 'We’d all been friends for years and my husband knew about it, too. She said she got pregnant from a guy she dated for a month.' Nicole invited her over, worried she would be feeling vulnerable and lonely.'I left them both in the living room and went to get some more wine from the cellar but came back when realised I didn’t know what everyone wants. When I walked into the room, I saw my husband holding Amanda close and stroking her hair. My first thought was, "That’s sweet" because they were good mates. 'It was their reaction that gave it all away – they sprang apart like they’d had an electric shock. They weren’t expecting me back so soon. That was when I knew the baby had been his.'CONVERSATIONAL CLUESIt’s hard work keeping secrets or pretending not to be as intimate as you really are.They know things they shouldn’t. Alarm bells rang for a friend of mine when her friend mentioned something about an argument her husband had with his brother. 'I mentioned I might ask Tom to have lunch with us all that weekend and she blurted out, "Are you sure? After what he did to David?". I knew they’d fallen out over something but there’s no way she could know... unless they were chatting without me around.'Their reactions are suspicious if you call them on something. Guilty people over explain. When my friend asked her best friend how she knew about the row, 'She came up with the longest, most ridiculously detailed explanation of how they’d bumped into each other on the street. If they really had, she’d just say, "I bumped into him on Wednesday and he told me'."They’re making inside jokes you’re not in on. Suddenly laughing over things you don’t quite get. Or calling each other by a nickname that didn’t come about while you were around. It’s hard work keeping secrets or pretending not to be as intimate as you really areLOGISTICS DON’T LIEEmotions can be tricky to analyse but the diary rarely lies.They’re both unavailable at the same time. He’s at a work thing so you call her to ask if she wants to meet; turns out she’s got ‘a thing’ on. He’s off on a stag weekend in Prague; she’s gone to visit her granny in Greece.Their stories have holes. You run into the guy whose stag do it was and find out it was a one- night party in London. Her grandmother calls when you’re with her and says, ‘When are you coming to visit? I haven’t seen you in such a long time’.Friends have seen them together – and they’re nervous telling you. Someone mentions – hesitantly – that they saw the two of them having lunch or sitting together in a car that’s parked. There’s always an explanation ('She was giving me a lift/We just bumped into each other, and both hadn’t eaten.') Why did neither of them mention it, then? Innocent encounters get reported back.WHAT TO DO IF THE EVIDENCE PILES UPFirst, breathe and take a moment. A single clue is not a verdict and if you’re prone to jealousy, chances are you’ve taken that and run with it. If, instead, you’ve read at least four or five things that ring true, do this:Keep an open mind: A friend withdrawing might be having a crisis she can’t tell you about. A secretive husband could be planning a surprise. Sometimes two people just really get on. Assume there are innocent explanations and see how it looks to you then.Start writing things down: Dates, details, what was said, what wasn’t. This isn’t for the divorce lawyer, it’s to make sure you’re thinking clearly when feeling emotional. It will help separate what’s happening from what you imagine is.Ask someone you’d trust with your life for their opinion: Preferably someone who knows your partner well, has a good sense of your friend and can keep their mouth shut. Are you imagining something that’s simply not there?Confront your partner, not your friend. Her instinct will be to deny it – and then warn him. Instead, ask your husband a clear question calmly. Look him straight in the eye and say, 'This is going to sound silly but are you and Rachel having an affair?'. Watch carefully for his response. He may well look startled and alarmed: if he’s not cheating and it’s never even occurred to him to, this is normal. So is anger: it’s not pleasant being accused if you’re innocent. But if, instead, they look sad, guilty or pause a little too long before denying it, your instincts were probably right.You’ll find more of Tracey’s advice at traceycox.com and @traceycoxsexauthor.SIDEBARTHE TELLTALE SIGN THAT HURTS THE MOSTIf your friend is cheating with your partner, it’s likely she will withdraw from you. Why? Guilt, of course.She used to text daily, now she responds a day or so after you do because ‘she’s so busy’. She’s curiously uninterested in putting dates in and no longer confides in you. You feel a distance you can’t explain and – ironically - often tell your partner about it.Priya, 41, said her friend ‘kind of ghosted her’ about six months before the affair got discovered. “I told myself she was obsessed with her new boyfriend and just in that ‘in love’ stage. I’d joke with my husband that she’d come running back when the spell wore off. When it all came out, I felt like such an idiot. They must have been laughing behind my back.”The reverse can happen too. Some friends send uncharacteristically soppy messages saying how much they love you in guilty moments or buy expensive presents.SIDEBARHERE’S HOW I DISCOVERED MY HUSBAND AND FRIEND WERE CHEATING...I asked women to tell me how they found out about a secret affair. Here are some of their stories.'He became oddly protective of her. If I criticised her, he’d leap in to defend her – way more strongly that the situation merited.'Farah, 28.'I noticed she’d dress up and put makeup on if he was around. She’d never bothered before.'Natalia, 39.'She started asking questions about our marriage. "Are you two OK? Are you happy?". I think part of it was testing to see if their affair had had an impact on us – obviously hoping it had. The other reason was to get me to doubt that we had a happy marriage.'Elizabeth, 32.'Mine was the cliche: he was guarding his phone and never had before. Screen turned face down, notifications silenced. I checked his passcode and it didn’t work. It was painfully obvious he was up to something, but it still felt like I’d been punched in the stomach when I found out it was with my friend of 27 years.'Anya, 48.'My gut told me. I started to feel incredibly anxious. I had heartburn for the first time in my life and was shovelling back antacids. Then I thought, ‘I’ve never felt like this – why now?’. I realised it had to do with feeling uneasy about my relationship. I was right to be. I found out plenty of people discover betrayal with no evidence other than gut instinct. Your body knows.'Leah, 36.