I'm dry before my boyfriend and I are about to have sex. What can I do to fix this problem?

Every once in a while I will have a problem staying wet when I'm having sex with my boyfriend. I'll start out wet, but then will dry up and we will have to stop because the condom will break or it becomes painful for him? Is this normal? What can I do? Please help, I love him so much and I definitely love having sex with him, but I don't know what's going on? Thanks!