Hi Op
I am so sorry you are going through this awful time.
I pretty much wrote your post 5 years ago word for word and the time I spent beating myself up that I had been responsible for my then H falling out of love with me lasted for ages no matter what anyone else said and it took me a long time to realise it was not my fault.
I blamed myself for not paying him enough attention since having a baby
I blamed myself for being too moany about work getting me down
I blamed myself for not being 'fun' enough for him any more
I blamed myself for not listening to him when he had tried to tell me he was unhappy ..
I did all of this because he had told me that these were the reasons that he no longer loved me in the same way. I did what you are doing now ( understandably) and felt responsible for him falling out of love with me and that 'if only I had been more x or less y then he would still love me. I was, like you completely blindsided by all of this and so it really was a case of kicking me when I was down.
I later went on to realise that all of these accusations were conveniently manufactured to suit his situation . There was an OW in our situation that he had met at work -they are almost without exception someone from work as ,like you say with young children there isn't a lot of time.
I, like you had been encouraging him to go out with people for work as he had recently been promoted and was doing well at work and he had started 'staying on friends' sofas' too.
I know it's not what you want to hear and yes maybe there is an element of him feeling like he has taken on too much too young (his actions are still inexcusable )but I would be very surprised if no- one else was involved ( and yes I was also sworn blind to that there was no- one else)
Anyway please don't do what I did and become almost obsessed with trying to find out of there was someone else involved. I now realise that it didn't actually matter. He massively shirked his responsibilities and was gone- making me feel like shit in the process like you are now.
Instead remember
He is the one who has bailed out of your relationship here. You have just been doing what every other mum to young DC is doing . Getting through each day
You are not responsible for this breakup.
Try and disengage from him and any more of his ramblings designed to make you feel like shit and him alleviate his guilt.
I am really sorry that this has happened to you at a time that was meant to be so happy. So many prole told me when it happened that 'if it was going to happen then far better now than when the DCs are older ( DD was 2, I was pregnant with DS) . I felt like screaming at people at the time but they were so right.
Your future H would have done this at some stage if it wasn't now and it would have hit you all even harder.
I'm still very sorry you are having to deal with it at all though.