End a 10 year relationship or not?

Warning this is long

Back story first, I met the man I call my husband (not legally married) right after getting myself and 2 children out of an abusive relationship. I was swept off my feet and thought he was the best thing that could ever happen to us. Fast forward 10 years and 4 children later, I now have a 15 year old, 13 year old, 8 year old, 6 year old, 2 year old, and a barely 3 month old. We have had our ups and downs like everyone but this time I don’t know if I should forgive and move past it or end it and take on the role of a single mother?

So, he took a trip 2 weeks ago to go back to his home town and pay his respects to a friend who passed away unexpectedly and he was unable to attend the funeral. When he comes back he wanted comfort which I expected. I really haven’t been in the mood for love making since I had our newest baby in January but figured hey if it helps him out of his slump why not give in this time. Now I wish I didn’t, in the middle of sex he comes out and confesses to sleeping with an old high school friend, so happens to be the wife of the friend who died. He tells me that she has always had his heart and I have his soul (whatever that means) in that moment I was completely devistated and felt like the last 10 years has ment nothing.

So I did some snooping around and he is logged into one of our tablets on his FB, I pulled up his messanger and proceeded to read messages between him and her starting the day her husband died about 2 months ago. Starting the day of the funeral they begin talking about how much they have always loved eachother and 2 days later they start planning for him to go see her to see if the love is still there. He tells her that she has always had his heart. In this moment I feel even more betrayed. I went through his phone as well and found that he has been calling her after work before calling me if she doesn’t pick up, then he makes up an excuse to let me go when she calls him back and makes an excuse for why he doesn’t come in the house right away.

I confronted him about everything this weekend even telling him I read all the messages so you can not lie and tell me it just happened when you went because you were both horny and she just lost her husband. His response was that the messages mean nothing he is just playing along to help her feel better and grieve and that he will stop if I want him to. I told him I want him to not only stop but tell her about me and the kids. She should already know this as they are FB friends and she congratulated us when our newest was born and his relationship status says married since 2011. Well I haven’t looked to see if he really did end things but I know she kept trying to FB call him yesterday and he was ignoring the calls.

I don’t know if I should trust that he ends things and just try to move on or take the kids and leave. To complicate things further I have not worked since before our 2 year old was born and don’t have a good support system where we live. So I would have to move 600 miles back to family and friends.