If you're going to have your protagonists literally s*x traffic a minor and have it be seen as a good thing, put a little more effort into making it feel justified. There are a lot of ways to get revenge that don't involve mimicking minor villains in tr*shy isekai's, so if you are going to use s*x s*avery as the method of revenge, you gotta earn that as an author, otherwise it comes off way different than I think is intended. If the main characters are morally gray already, then it could work. If the characters are supposed to come off as upright members of society, maybe don't have them do something that should horrify any decent person? Just a thought.

Ex girlfriend’s whole family destroyed, was chased by Yakuza for more than 20 days and ultimately forced to prostitution after being caught by them. All of that’s indirectly caused by FMC

discovers his gf going into a motel with an old guy and the next day she tells everyone that he was the one cheating, no one believes him, not even his mother, and he was going to kill himself, yet just as he's about to jump from a highway, his childhood friend that he hasn't seen in years finds him, and, surprise surprise, she's rich. This all happened in the prologue, so it's not like it's a big spoiler or anything.

Being rich makes it hard to make true friends, so many people would want to use them like an ATM, a popularity booster or at least an emergency liferaft for hardship. They'd almost certainly attach great importance to people they see as true friends that aren't after those things- and romance coming from it isn't a surprise even if the memories are small things to us they aren't necessarily small for others.

MC became a butler because he wanted a part time job instead of taking advantage of his friend; not everyone's comfortable being a 'neet' or a 'salted fish'- and better yet for the FL she just happens to be allowed to take one escort with her to school and as someone that clearly wants him around of course she'd offer it to him and he'd accept. I don't see anything all that wrong with it.

As to the revenge being too harsh... Yeah that's true, she's crazy; even before the revenge bit she has her staff knock out a guy and drag him some random place just so he's not an eyesore on their picnic in a park, but it's an endearing insanity.

It's not the most unique, I agree with that too but there are almost always a few knock offs of any decent lightnovel and some of them are good like this one.

As to the MC liking the FL too quickly.. She was his childhood friend and when everything went wrong in his life- his girlfriend cheating and lying about him being the one that cheated turning everyone including his own Mom against him and is about to jump to his doom she saves him, takes him home and gives him a job, friendship, comfort and hope- there are worse reasons for love honestly!