I need help!! Please!

hey there, i dont know if anyone is gonna reply this, but i could really use your help, and of course, this is about a guy.. Last year i was crushing a friend of mine and we hocked up once bc he didn't want anything serious and i was really sad about it. I tried to forget him and it worked, and a friend of us started to talk to me and we hooked up. But this friend happens to be the best friend of the guy that I liked and one week later after  I hocked up with his best friend we were at a party and the guy that I liked told me that he wanted me and we hooked up. But he doesn't know that me and HIS BEST FRIEND had a thing ONCE. And now we are seeing more of each other and every time i'm with him, i want to tell him but i'm afraid that he doesn't want me anymore and it's very possible that he doesn't want me anymore if I tell him, but i'm not being a very good person if i don't tell him. Someone please tell me what to do, im completely lost and confused.