Pregnant and very clingy with my boyfriend?

Okay.. So I'm 20 weeks pregnant and I can't seem to stop worrying about my boyfriend. Since we've found out he's stopped doing all of the things he knew were wrong. Such as smoking weed and drinking constantly... But sometimes he slips up.. Like he'll go hangout with one of his dumb *** friends and go smoke.. And it really pisses me off. I can't trust him in that sense but I know he's trying and wants to be in my life and this baby's life. Hes twenty.. And this baby wasn't planned, but he's told me many times he loves her already. But how do I stop being so over protective? Or do I have the right to be?