Trust issues

My boyfriend of over a year struggles with trusting me . It seems like once a week he is accusing me of sleeping with someone I don't even know. At first he said it was because we weren't having intercorse enough. Then it was because my phone was always dying, then it was because I would lag a few min replying to his text and now it's just getting out of hand to where he is embarrassing me in public by saying rude disrespectful things. Don't get me wrong he isn't always like this . Most of the time he is very sweet but at times its overwhelming the things he says to me (calling me a whore or a stupid bitch) I just don't know what to do to ease his mind I have been 100% faithful to him . I spend every waking moment texting or on the phone with him . We live together and I try to be everything he expects of me but it just never seems to stop his trust issues . I am at the point where I am Desprare for advice .