Oh geeze. I'm sorry to hear what happened.

It's not your fault though. People move on with their lives, your boyfriend couldn't live with his mom and keep her company forever. What she did was incredibly selfish and hurt a lot of people, but right now the worst thing would probably be for you to leave your boyfriend. He just lost his mother, he might not be able to stand losing his girlfriend too.

My husband's parents got divorced a few years back when we were still dating. I felt similarly, that here I was stealing her son from her after she had just lost her husband to an old from of my husband's. I felt like it was my fault completely. If I hadn't been interested in Travis, he would've probably dated this other girl, which means she wouldn't have been free to screw his dad and ruin his family. I think it was her way of getting back at Travis for turning her down. That said, I know deep down the divorce was the fault of this other girl and my husbands father, but I still felt responsible in some way. It got to the point where I was so depressed about it my husband sat me down and forced me to tell him what was wrong. Maybe you just need to talk about it with your boyfriend.