I don't think so, most of the characters presented in the game that are in a relationship are either old timers, farmers who lived all their lives in the Mojave and just survive day to day like in the Old West. Basically, they live their lives day to day and struggle by struggle, the Mojave crisis being an other one since the last battle of Hoover Dam. A big scale war is also way more different than living in the wastes (and arguably way more dangerous).
Most couples in the game don't end well too, especially when the Courier is in the scene. He is litterally in a war story, there is widows left and right, broken men like Boone or that drunken wife beater who had all his family ensalved because they run away from him (bad luck and Vegas, typical). This could convince the Courier why settling down right now isn't a good idea, at least its my head-canon.
I see no reason for Fallout 2 tho, the stakes for the game is way more low, the atmosphere and personality of the Chosen One can really be open on that. Shame romance in that game was just treated as a really good joke in Modoc. I heard they did tried to recreate that scene with Cass in FNV tho, but Chris was strongly against it.
Edit : One could argue that if the Courier let go of his revenge against Benny and remained in Goodsprings, he/she could be happier. but we enter in fan fic territory, but I like that it remains in the theme of the game, letting go and all that. If we had a type of failed romance like in RDR 2, I think it would be more interesting than just having our self insert character loving a character we like.