My boyfriend doesn't consider our relationship to be serious, what should i do?

My boyfriend doesn't consider our relationship to be serious. We've been together for over a year, both of us have met each others families and been to each others hometowns. We've talked about marriage & our future together. Currently we are doing the long distance thing. I recently broke up with him about two weeks ago before i left to come home because he told me he thinks he should still be able to have "female friends" which aren't really female friends at all, but really just female associates. He told me that he doesnt think our relationship is serious enough for him to stop befriending or associating with females. We ended up getting back together before i left because he wrote me a letter saying that he doesn't mind letting go of these female friends. He claims having and talking with female friends is who he is, & me not being happy with it shows i dont like who he is. I cant sacrifice my feelings to be in this relationship. & im not sure that hes even really willing to let go of these female friends. Just the fact that he doesnt see our relationship as being serious & i do bothers me. What should i do?