I've been regularly meeting this guy every week for casual sex. (We're both college aged males.) Generally, I give him oral until he ejaculates into my mouth, rim him, and then we will have anal sex, and he will ejaculate in me. Every time I rim and suck him, the next morning I will have bumps/sores around my mouth. The bumps go away completely in a couple of days, and this does not happen when I do this with anyone else. Just every time I'm with him.
What could cause this?