Ren is a lucky guy... but you know what... Sumire is really lucky too, because only a guy with his physicality to endure the "needs" of a vampire gal.
I hope in 1000 years Sumire still remembers the man she loved... but I hope too she lives her life to the fullest, she deserves to love and be loved even after saying goodbye to him.
It may sound fatalistic, but I think that when someone who has a very long lifespan like her loves someone with a short one like him, she has the right to find love again, if she so desires obviously, I know that at least she will have friends at her side.