It's impossible to give any accurate type answer with the little information you have provided. We cannot tell you if he is using you for sex unless you tell us what your relationship is like, how often he sees you, if he calls you only when he wants sex, that kind of thing.
The only advice that would (IMO) be accurate is that a guy cutting himself to "prove" his love has mental issues and you should be very wary of or avoid someone like that all together.
“The willingness to accept responsibility for one’s own life is the source from which self-respect springs.” ~Joan Didion