I've been with my OH for 3 years and we are expecting our first baby together in October. V v happy and excited and our relationship is great bar one thing that has played on my mind since Christmas that I can't seem to shake.
My OH went out for the night with his friends and ended up getting stupid drunk. I didn't hear from him until 12.30pm the next day and he also didn't go home that night (this is before we lived together so I didn't realise until I spoke to him). He told me he got really drunk, met a guy in a casino and ended up going back to his house 20 minutes or so from us, carried on drinking and fell asleep with a dead battery. This was honestly fairly believable with him in the beginning as before we were together he had a tendency of getting really drunk and ended up in random places (this all stopped once we got together and was the first incident of its kind in our relationship). I was really angry and upset with him as I'd been so worried but after a row and some coldness from me for a day or so we made up and moved on. Fast forward a week later and he left his phone in his room whilst he had a shower. For the first time ever I thought I'd check and see, as I still had some niggling doubts about the week previous (don't judge the phone checking - we've all been there, done that). In his WhatsApp calls were 3 calls on the night he went out to his ex girlfriend. One was her calling for 1.30 mins, then him half hour later for 3 minutes then her calling her an hour later for 10 minutes. I checked the profile of her on WhatsApp and she was muted at a time of 1.30pm the next day (the time he got in). I confronted him straight away which resulted in me walking out of the house and a row that lasted a good few days. He claims it was nothing, he had seen her on the train up there and was just drunk so didn't want to seem rude when she called him etc. I was obviously upset and hurt as he'd gone missing that night so I accused him of being at hers which he denies and still denies to this date. I've bought the situation up about 2 times since then when I've been having down days and feeling anxious. Still very much denial and there is no way on earth that that would've happened and he would've never done that to me.
Thing is, it's been nearly 8 months and I still don't know what to believe. Did he go back to hers? Did he sleep with her? Is he telling the truth? Why did she call him in the first place? Questions I ask myself all the time I have no answer for!
It honestly runs through my mind once a day and is really bringing my mental health down as I really don't think hes telling me the truth. I do trust him but I just don't see how it didn't happen. Which is really upsetting because in every other aspect of our relationship I can't fault him and obviously we are having a baby together so I really do want things to be good.
Do I sweep under the rug and forget? Go off my instincts and sack him off? Message her and see what happened?
I don't know but I do know I need to get this out of my head as it's affecting me every damn day. 
Sorry for long post x