Can I really do this?

So I’m 7 . 5 weeks and my boyfriends ex decided to tell him I’m cheating on him and this isn’t his baby . It’s absolutely not true and she cheated on him and ruined him he has never trusted me in the 3 years we have been together . And they have a son together who I love and cherish as my own . But this girl friggin intimidated me and now she is trying to rip us apart while I’m pregnant ?? I’m freaking out he won’t drop it , and he can look for proof all he wants he won’t find any because I didn’t do anything. But just the stress , I almost want to leave him so I won’t have to deal with her for the rest of my life and I wanted this to be a happy time I’m not sure I can do this .