When Do You KNOW?

So my SO and I haven't been together very long but, since getting together we've seen each other every day. We have the same taste in music, an amazing sex life, can talk for hours... I've never felt this way about someone before. Recently we've been talking about marriage, he got me a beautiful promise ring/engagement ring and says he's ready to settle down and start a family.

How long have you been with your SO? When (if) did you get married?

Advice?