My boyfriend's parents think I am tricking him?!?

Gabriela • First time mom. 23. Due 06.26.17
My bf and I use to live together and he broke up with me during a period we were still living together. He ignored me and treated me bad, and I started texting guys and he found out. He acted as though I had cheated physically with someone else which I didn't. Plus we were broken up. So, now I am pregnant with his child and his parents were asking him if it was his. As though I would do something so fucked up like that. Not only lie to him but make my child believe he is the father if he isn't. Like for them to think that makes me feel bad. And my bf doesn't understand why I feel offended. He says that they knew I was talking to other guys because he told them. Though I just did that "one day"! I never went out with anyone or anything. 
Idk if I even want these people in my life who think such things, plus we were broken up. He probably made it sound as though we weren't to make me look bad. Now I'm worried that when our baby is born, his parents will always think it's someone else's. Even though we were having sex this whole time, I'm only 8 weeks pregnant. And the talking to other guys shit happened about 3 months ago. 
What should I do? 
The baby is HIS obviously!