I am sorry but that plot reeks of fan fiction amateur level of writing. Not that official fallout 4 games writing is much better beyond quirky humour.
Out of all the simple run of the mill stories that video games use, especially in the cases of romantic stories. The only one that has good writing in romance I have seen so far is in Final Fantasy Tactics, there is a reason they keep remaking and porting that game. Though something of note is the "main" story line is boring normal FF game stuff, but all of the sub plot regarding class struggle, family allegiance, and romance is top tier.
In short, there are three major characters in that game. Ramza, who you can rename serves as the player's prospective as a nearly silent protagonist. Delita, and Ovelia are the other two. The player, Ramza, who you can rename, shared an childhood with Delita. Though they were best friends and even joined a militia group together, the player is from a noble family and Delita is a dirty commoner. After Delita's sister is murdered he decides to go seperate ways from his childhood friend.
Some years later the player is put in a position of protecting the princess Ovelia from the prince as a mercenary. With both support from the player's noble family who seeks to benefit from the player's ties with the princess and also the support of the player's mercenary group the player is wholesomely invested in protecting Ovelia and putting her on the throne. With the player's noble birth and time spent together you would expect the beginning of the love story to go well. But as art imitate life not everything is so simple.
Things go wrong and Delita, who is working with "the bad noble guys" now shows up outta nowhere and kidnaps Ovelia. Delita at this point comes off as a driven no non-sense character, who has climbed to the top of the military ranks on his own merit. Delita also gains Ovelia's trust eventually and they marry. Delita eventually becomes king with his marriage to Ovelia and is loved by all as the hero that stopped all the fighting within the kingdom. While in reality, it is the player who foiled multiple plans from multiple parties to claim power. The Marrieage between Delita and Ovelia does not end well either. Ovelia who realises that she had been used in the end tries to kill Delita. On her birthday she meets with Delita at the location where they first met. Delita brings her flowers while Ovelia stabs Delita with a dagger. Ofcourse Delita takes the stab like a man and in return kills her with her own knife. The last scene is Delita looking at the sky with Ovelia dead in her arms. A naive girl if allowed to live would send the kingdom into civil war again. But in this last moment you can sense that Delita is conflicted in that he killed a girl just like his sister, who's death was his whole motivation to stop the kingdom from fighting and take his destiny into his own hands.
The story though dramatic is quite mature in that it is similar to how love is in the real world. A girl leaves a guy for a better guy, someone who is more driven and more wealthy. She regret her choice in choosing wealthy, comfort, and security over feelings. They divorce... The guy who is sincere and equally hardworking sometimes does not get the girl, or the recognition, but in his mind he is at peace because his actions dictate who he is, not his circumstances. The wealthy driven guy loses his wife, and has to confront the reality that in his pursuit of worldly thing he has neglected someone he obviously loved at one point. But in the end no one is at fault, all the characters are well written that they do the things anyone would do if put in their shoes with their past and motivations.
This is adult relationship in a video-game. This is also why I never play "story" based games, as the stories are always so bland and simple compared to novels, films, heck even documentaries.