But we've been together for a year and a half...living together for 6 months and now he says he isn't ready for marriage. One day, but not now. I don't want to pressure him, but feel like he changed his mind.
no he didn't, you need to wait, he mite has plans on finishing school or something. i mean you guys are together and live under the same roof, don't pressure him or he will leave.
After 2 years, he should have an idea of "when." If he doesn't want it to be now, I totally get that... but letting you go on with some vague notion of "someday" isn't fair.
Pressure away, I say. Let him know that you did NOT move in with him to eternally be his cow from whom he gets milk for free. Tell him you think he went back on what he led you to believe, and that's not cool. If he wants to wait until some specific milestone has been passed (like graduating from college, or turning 25) that's fine, but you need to know.
Also consider moving out and living with female roommates instead. If you didn't discuss and agree on marriage plans before moving in, you made a mistake to begin with.