the only reason he is apologizing and "maybe" regretful is because he is not happy and his boyfriend is not completely with him. If he was happy with BF he wouldn't have had a single thought of River.
UPVOTED 100x. His only regret was that his lover was dead (as in no longer responding and having no emotions), and now tht he had also killed off his other lover, hes trying to get him back too. If thats not being greedy and selfish then Idk what is
Finally