Am I just a rebound?

Hey! So I started dating this guy and we’ve been dating for a little over a month, and were talking for about two months before that. Everything has been great and he’s a really nice guy, but I know that he got out of a longer relationship around six months ago (not 100% but I think it’s in this ballpark). He never talks about his ex, won’t even say her name, and the one time some of his guys friends brought her up he told them to shut up and got all sad afterwards. I’m not sure how long they dated for, but I do know that he had liked her for a long time before they even began dating. I want to be there for him and give him support if I can, but I also don’t want to “just be a rebound.” Do you guys think I’m just a rebound? And if so, what do I do?