Sirius might have thought he didn't deserve him, but Remus felt that he was the one undeserving. Sirius could have anyone he wanted, and he chose him -- a werewolf. People like him just didn't end up with fulfilling relationships, but Sirius loved him. He didn't deserve it, but he couldn't help himself from accepting it because he loved Sirius so much.
Remus brushed their lips together again, and held onto Sirius. His hands shifted so that one came to rest on the other boy's hip, while the other slid up into his hair. "Sirius.. No matter what either of us deserves, we're here together." He placed a tender kiss against Sirius' jaw. "And I love you."