I don't know what he wants?

If he were using you it would be for steady sex and a sense of security.what I see from what ur saying is u guys dont really have solid communication and if ur the only one who has mentioned marriage then he definitely doesnt want to.hes blowing u off because he knows ur not going anywhere.if u have to nag or beg someone to commit to u do u really want to spend the rest of ur life in a bitter, resentful marriage? If there was a future he would be mentioning the topic as much as u or at least engaging the conversation when u bring it up.ur too young to"settle"for someone just cuz hes been around for a while.