How do I build a relationship that will last forever? Will premarital lead to a breakup?

Im 19 and my boyfriend is 23. We've been together for four months but it feels like I've known him forever. I love him soooo much, when I'm with him I feel safe & free to be myself. He is my first boyfriend but I dont have any desire for another. I want him to be the man I marry. I am a virgin but I don't have anything against premartial . We both want to do it, but he says he will wait for when I'm ready. We also talk about living together once I graduate college in four years and then getting married when I am 23 and he is 28. I love him so I want to do these things, but I dont want them to lead to us breaking up, I want to get married & stay that way. Alot can happen in 5 years, but I want us to feel the same about one another. Advice?