My boyfriend says he doesn't like to do things with me because we fight too much

He owns his own business. Sometimes, he stays out all night but doesn't tell me. We have a son together, and I get to stay home with him. He says I complain too much about what he's doing. We've been together a year and a half. I got pregnant after being together for a month. We moved in together when I had my son in July. Everything was great, and then he started the staying out. He then started not spending time with either of us. I just don't know if I'm doing something wrong. We've talked and he says this is just how he is, but he wasn't like this before.