Slowing down

So my boyfriend and I have been together for almost 4 years now. But we grew up as neighbors so our families have always been really close. I wanted to save myself till marriage but I ended up caving in and having sex with him. ( not saying it was / is bad ) it's just that I want to wait till after we get married. He is constantly saying he wants to someday get married but when I mention the topic on waiting till then he rushes to change the subject. Any advice on how to approach the subject?