“Heartbroken” MMC “settles” for family friend or wallflower

I’ve realized that I really really like the stories where the MMC has decided he will “never love” or “never love again” because his first love either betrayed him, or happily married someone else. But since he needs an heir, he chooses a family friend, or a wallflower (who will of course be faithful, because who else would want her?) I only like this when the OW is not a threat at all to the main couple.

I really like the moment when he realizes that he fucked up and is actually falling/has fallen for his wife.

No cheating, no betraying of marriage vows.

Recommendations please?