Lover Eternal by J. R. Ward Black Dagger Brotherhood

Rhage is the brother with the strongest appetite and he's the best fighter the Brotherhood has. Mary Luce is a woman who doesn't have much time. One night while talking to her friend Bella a young man appears who Bella recognizes as a pretransition vampire. Through the young vampire Mary and Rhage met and Rhage automaticly reconizes Mary as his Mate.

This is the second of the Black Dagger books and more emotional than Dark Lover. The pain that brings Mary and Rhage together really gets to you.