I need your advice!

I swim for exercise. Every night the same guy follows me into the shower and stands next to me with a big erection.
A few times I've let him touch my Dick. The other night he asked if I wanted to follow him to a family change room. I said yes. We sucked each other and played with our cocks. He fingered my ass while he jerked off and came all over the floor.

Now I have to see him all the time I think he wants to fuck my ass. I've never done that before and I don't know if I should let him. When I see his hard cock I get so turned on.
What should I do? Last few nights I've ignored him...