Don't know what to do for the best

I don't really know where to start but me and my oh where going through a rough patch, work money the normal stressful things, we have a 3 year old little girl together and we are expecting are 2nd bundle of joy in April, but from all the stress ect, after our scan last Tuesday he decided he couldn't do us anymore and called time on our relationship he needed space and also stayed on the sofa, I gave him space with now is clearly the wrong thing as he said I should of tried to save it, then on Saturday he went on a work night out invited a couple of his own friends  along to, I then find out that the only person from work went was a girl that he talks about a lot, and loads of her Friends, turns out it was for her Birhday and she is in fact single witch he told me she was not and still in a relationship, anyway Sunday morning,  wrong I know I went through his phone to have a look they text about having a spoon and she said she should of come in, (I stayed at my mums house that night) he also said she has a hold over him! I went mad a kicked  him out, but my problem now is what do I do, I love him so much and I relise now  are problems where deeper then I first thought but he also says he feels guilty for maybe stringing her along, witch winds me up as why is he bothered about how she is feeling!  and now I feel like I'm being punished for something he's done, I do believe nothing happened but the thought was there and he clearly finds her attractive, they work together 5 days a week! ... I don't know what to do, I don't even know what I'm asking .. We have a home together a child and a baby on the way and I feel like the bit of attention was worth more then his family!