When does a relationship (become a marriage) ?

ok guys so i have been with my boyfriend for 10 yrs, we live together e.t...c. now suddendly this asshole for lack of better word, wants to move out and be with somone else....he now says we were never boyfriend or girlfriend that we were just friends all along....so when is a "relationship" considered a marriage even when u r not really marry? is there any legal actions that can be taken on this? pls no flaming...I'm confused with all this, hurt and crushed, need some simple knowledge from anyone.