SO has REALLY bad anxiety.

So my boyfriend has really bad anxiety and I know he can't help it but it's really hard on me. He is so paranoid and comes up with off the wall accusations randomly. Also, I can't joke with him about anything without him freaking out on me. One time I wanted to go to my moms and he freaked out and thought I wasn't coming back home. I just need to know how to talk to him about it because most of the time I try to buy it just makes his anxiety worse. He knows it's hard on me and he feels really bad and he's trying to control it.