Confused and frustrated with my boyfriend!

I have been dating a guy for a year and a half. We had a great relationship at first and then he did a 360. He seem to pull back away. He has an ex of 17 years. They have 2 kids one 18 the other 8, he doesn't want me around when the kids around and he won't tell his ex he has a girlfriend. I was ok with him helping her cause she does have his daughter. But now it's the hole secretive thing has gone on way to long. I fell for him so now I'm the one always hurting. I also found out recently he cheated on me. I have tried to move past it my heart won over my head. Just not sure anymore of where we are. Everything has changed.