My boyfriend of 26 years has left me forever?

Okay so I'm 41 and I had been with my ex boyfriend since I was about 14 and we've known each other since we were about 12. I see marriage as just a piece of paper so we never got married but we were committed to each other and we were together seriously, not off and on, I mean it was like we were married. I was told by several doctors that I'd never have children and I don't want children so we never had any kids and things were pretty great for years. I guess things started to fall off about 6 years ago, right after he turned 35. He was having a "mid-life crisis" phase, you know wanted a motorcycle and all that other crap that happens but we started to grow apart. Things that we never thought twice about, became the topic of our worse fights but I didn't think it was that bad. Things weren't as good as they used to be, but they were still good. He would then bring up all the things we could have did years ago that we don't have time for now which was odd because he's not the type of guy that's stuck in the past. We began drifting more and more apart and spending less and less time together over the years. One day we had this stupid fight and he was about to leave and I just said who was she. I had not even thought he could be cheating until the moment I said it. He said that he wasn't cheating but that I was selfish because our whole relationship was based off what I wanted. I told him bulls*** and how in the hell he had come to that conclusion and he said that he gave up a lot to be with me getting married, having kids, and a bunch of other things I thought didn't matter to him. I told him he chose to give up those things and that I didn't force him to and he told me that he was tired of him giving me so each and me giving nothing and I said that he could leave then. We didn't talk for a few days and I moved all my stuff out of the house. I was so angry at him, I mean how could he blame me for that? After we cooled down we talked and decided that if we wanted to save our relationship, we needed a break so I officially moved out to a town about an hour away just to get away from it all. We decided not to talk at all after a month because all we did was fight. Over the next 8 months, I reflected on us and I realized that he was right about some things and that I was being selfish. During that time, I kept hearing that he was sleeping with a co-worker but I didn't want to believe it until I finally called him after 8 months. He was happy to hear from me and we had lunch. I confronted him about the rumor and he said that a) he had slept with her and b) it was time to end us. I asked why and he said "because I have something more important in life to worry about now. A baby." I wanted to throw up when he said that.How could he get someone else pregnant. That just made me mad. I started screaming at him and he said "we didn't talk for months, so its not really your business." I asked did he love her and he said he's starting to fall for her and that its best we didn't talk anymore. How could he throw away a 26 year relationship with his supposed best friend for some 25 year old skank at his office and her kid that he doesn't even know is his? I'm so hurt now. We haven't seen him in about a month but I'm so depressed and humiliated. I've never been with anyone but him so I don't know how to start over and I would do anything to be with him? How am I supposed to cope with this?