Sorry, this might be long. Please be gentle, I'll try not to dripfeed. I've name changed as some details could be outing and I don't want anyone in RL to link it to my usual username.
To cut a long, messy story short, last year me and my husband went though some BAD times and I had some of the classic lines 'I love you but I'm not in love with you' 'I don't know what I want any more' 'I don't know how I feel' blah blah blah. Now having seen 'the script' on here a fair bit, I know the next step is usually discovering an OW. And in a way there was, except there kind of wasn't too.
He had to travel occasionally for work, he's friendly with many colleagues who also had to travel for the same work - there's male and female ones, they've never bothered me but for some reason this one woman in particular just got my senses tingling. (They didn't work at the same office and don't live near each other so it was literally just these occasional trips when he saw her). He's always been very open with his phone and stuff so I've seen messages between them (not just her, messages with other colleagues too) but never anything untoward.
When he gave me the whole speech about not knowing what he wanted any more, I was understandably devastated and immediately begged him to tell me if there was anyone else or if he'd had an affair. He immediately admitted that he'd developed 'feelings' for someone else but he'd never acted on it and never would, but it had made him realise that he wasn't happy in our relationship. For a while I was convinced he was lying and that something had happened, I'll be honest for a while I was completely obsessed, I made myself ill over it, checking her social media etc.
I found out from his internet history that he'd been repeatedly checking her social media, even old unused accounts from years ago (good old Myspace!). He'd also googled a few odd things like 'in love with a woman but I'm married'. He'd even somehow managed to find her address and had googled that a few times. Like, as in, I think she's be COMPLETELY creeped out if she knew. I think this is when I realised for sure that nothing had ever happened with them.
In the end, I just got completely pissed off with him fucking me about and not telling me what he wanted so I told him I couldn't put myself through it any more and that he should just move out. It was all very messy and complicated for a while but eventually he broke down and admitted he'd just had a complete mindfuck, he'd been depressed and it had made him feel numb towards everyone and it had made him feel like he didn't want to be married any more and he'd just formed some sort of odd emotional attachment towards her because she was a nice person and was easy to talk to. (I will add that all through this, she also had a partner). I do know he'd genuinely been depressed as I found google searches about depression and suicide. He said he'd realised losing me would be the worst thing to ever happen to him and he wanted us to fix it and be happy together again. So we did some counselling and a whole lot of talking, it was very messy and painful for a while but I am very gradually feeling like we are almost getting to be in a good place together again.
I'll just say at this point - I know there will be posters reading this who will be thinking 'something definitely did happen with her physically'. I know the usual script and how men generally don't want to leave unless they have somewhere else to go. I'm not naive or an idiot, although it might come across that way. But I absolutely do know 100% that nothing ever happened between them, that's not what I'm wanting to discuss/find out here. He reckons she never had a clue of his feelings (although I think he might be a bit naive thinking that - I feel like us women are quite good at sensing stuff like that!). She's a few years younger, very happy with her partner.
I'm not sure what I'm asking here. I just still feel so betrayed. Even though nothing physical happened, I feel like he betrayed me in his head. He thought he was in love with her, he obviously had thoughts/fantasies about leaving me and being with her. He fully admits this and says he was an idiot, he didn't even know her well enough to be in love with her and he was just an idiot with a stupid crush. Up until last year we weren't very good at talking about our feelings and about our mental health being shit and so he kept it all in and it just spiralled inside his head.
It's been months now and since then he's put so much into proving to me that it's me he wants. He is attentive, give me affection, compliments, and that's been consistent. He's got help for his mental health and he has changed things at work so that he doesn't have much contact with her (he is also looking for a new job). But there's not a day goes by that I don't think about it and wonder why his head was turned by her, I keep torturing myself wondering what it is about her that's so much better than me? How she's younger and has no kids so doesn't have a 'mum body' like mine 
it's totally killed my self esteem.
What can I do, how can I begin to get past this? (What can HE do to help me get past it?). We do talk a lot more now and so I am honest and tell him when it's been on my mind and bothering me but a lot of the time I end up crying and I don't want to have to keep doing that. He says he can't believe what he nearly threw away over a stupid crush. But to me it was more than that, it was like an affair in his head. I often wonder what would have happened if she'd ever showed interest in him. He swears blind it was a stupid crush and he'd never have acted on anything, he loves me, he's devoted to me, etc. But I'll never know for sure, will I? And that's what they all say isn't it.
What can I do so that this does't torture me forever? I've even contemplated separating/divorcing him. But the fact is I love him, we have children, and up until this we had many happy years together and even now we are happy together (aside from this issue!). I would really appreciate any advice. Thank you