This is what happens: he meets a guy in uni that is actually very smart yet sensitive, that he would understand and listen to him complain about things without trying to push him to do anything. He would make the uke feel so safe and secure. He also met some people and made cool friends that he feels very comfortable with.
In the beginning the seme would help doing the housework but little by little he would go back to his old ways: being pushy and selfish. He would push the uke to have sex for example, he would forget to do his dishes, he would also push the uke on dates despite the uke being tired while at the same time he wouldn't do activities that the uke finds fun.
I imagine for christmas day, or on the uke's birthday, he would buy the uke something that he, the seme, would like without really considering what the uke might like.
I don't really hate the seme, but I don't like him at all either, and I def think that the uke can do sooooo much better.
The uke would feel bored and very unsatisfied by the relationship. I am not saying it will be abusive, not at all, I just think that the uke might also slip back into compromising too much and he would end up getting sick of it all. Especially sick of the seme's stupid gifts that he put 0 thoughts into them.
At the same time, he would start catching feelings to that intelligent guy (or that girl, who said he can't be bisexual??). So once, after he fights (once again) with the seme, he finally cracks in front of one of his friends and so the friend takes him to a quiet bar so that they can wind down a bit and they meet with the other friends, including the new person.
He and the new guy would talk the night away with the new person who is very considerate and cool but a bit on the shy side. This would later on make the uke feel a bit more in control as well, since the new person would give the uke space to take his own decisions.
From that day onwards, the uke goes back home more and more late, and he kinda avoids the seme. Once, he is back drunk and elated, and completely ignores the seme who had been feeling lonely for a while. He is hurt that the uke doesn't wanna talk to him or makeup, and by the way the uke is generally acting cold. He feels super insecure but also angry, so he pushes him for sex, and this only makes matters worse. After getting touched for a bit, the uke tells the seme he isn't in the mood, so the seme only feels more frustrated and he starts to avoid the uke. At first, that tactic might have helped before since the uke was in love with seme, but now things have changed. This only brings the breakup date closer. The uke tries to meet the seme halfway and he ends up sleeping with the seme as a way to clear the air between the two of them. So, being the stupid selfish guy he is, the seme thinks that all is well between them.
One day, the uke invites the new guy home so that the two could work on a project, but the project is only an excuse for the two of them to chat and chill. When the seme goes back home and sees his boyfriend smiling so genuinely and act cozy and warm with another person, he gets insanely jealous, so he tries to mark his territory by joining the conversation and sitting very close to the uke. Except that, what the two talk about doesn't make any sense to him, and he feels like a burden. The fact that his boyfriend who had been neglecting him all this time is acting all chummy with another guy angers the seme so much. Especially with how the two of them looked as if they were having a moment.
After the new guy leaves, the seme confronts the uke, but he comes out more petty than anything. The two of them fight with the uke reminding the seme that he doesn't put any effort either, and they go back to fight about the same trivial things as before, except that this time, it is the seme who is angry at the uke as well as jealous. After the two of them keep arguing. He blames the university, and the uke neglecting his duties as a lover as the reason for why this didn't work. He goes and accuses the uke of flirting with other guys while he was still with the seme, but ofc those arguments only make the problem worse which makes the seme say "this isn't working anymore", and the uke agrees and tells him he wants to breakup, which is something that the seme had been very very very afraid of hearing, especially since he thought that all went back to normal between the both of them.
Oooh my dear selfish, stupid seme. If only you were more considerate and less egoistic, you would have seen the inevitable breakup.
Isekai, the usual transmigration, reincarnation, time travel etc. except, you know, it's gay