boyfriend thinks im cheating

idk what to do , my bf accuses me of cheating with any guy that just walks past. ok so a couple month ago a guy i don't know waved and i barely waved back just being nice but not friendly and walk to get my baby out the car. he says im fucking the nigga and accuses me of getting out of bed and unlocking the door like seriously? I don't sleep walk. he says is bc of me he don't trust me! So when we first got together I ask him for a open relationship but we had just got together, like he ask me out the first time we chilled! I just had a baby 2 month prior and just regrouping from my baby father leaving me with a baby! He puts me out just from the thoughts in his head! He literally got mad bc I pick up my phone! When I get on my phone he thinks I'm cheating! Idk wtf to do! then we are about to get a benz together but he will probably take that back! Lord give me strength