You have some choices. If this relationship is serious, as in he's the one, then look into counseling or sex therapy. If he's not the one, then ending it would be the best thing for both.
However, I do want you to consider something. While, yes, sex is an important part of a marriage, it's not the be all and end all either. By that I mean, say you marry someone with whom you have great sex. 30 or 40 years down the road he may end up with health problems that make having sex difficult, if not impossible. Is there enough to hold your marriage together should the sex go away? Do you love each other? Share common interests and values? Sometimes there is great sex and nothing else in a relationship. Take away the sex and there is nothing to hold the relationship together.
Strive to have both--good sex and a good relationship. Just know that things can and do change as you age.