When the guy you love destroys your family

About six weeks ago, my son's dad broke up with me. We had been together for about 6 years, friends for almost 8. We had some rough times, because he was in the military and was away for 4 years, but we survived that, and I truly thought we could survive anything.

It turns out that I was wrong. It turns out that apparently he wasn't half the man I thought he was.

Apparently, he had been unhappy for a few months. I will take the blame for that, I'm not perfect and I have some relationship issues I need to work on. But that's where I stop, because instead of telling me he wasn't happy so that we could work on things like mature adults, he acted like everything was fine and then went behind my back and poured out his problems to a random girl on facebook. And of course, after talking to her for months, he fell for her. I still haven't figured out his true motivation for ending our relationship, if it was because of her or truly just because he wasn't happy. But either way, I can't help feeling that he is a horrible person, and selfish, and incredibly immature. We have a child together, but this strange girl is more important than his son's family. And I'm not saying couples should always stay together for the kids, but he didn't even try. There are so many things we could have done to fix our relationship, starting with communication, but he never gave us a chance. And now I can't even just move on and forget him, because we have a kid. I'm not dealing well.