Couples hitting each other or generally treating one or the other like shit. Being struck is literally a red flag to get the hell away from them, end of story. Humiliating is also a sure way to make a relationship not work. If you don't respect and generally don't care if you publicly make fun of them, you will soon find your relationship over. This is why in real life Dom/Sub relations don't last. In the quiet of your bedroom, it's game on. But in public, where others can see you, there is basically no chance it will work.
Most romance comics are not real people at how they act and the like. Misunderstandings are fine for immature relationships (highschool), but once you live life for a bit, you just tend to talk it out or leave.
The guy or girl that can't decide on two different people, usually gets neither. And specially for a guy, he who plays hard to get, gets none. Girls don't put up with that in real life. That is why harem anime/manga are annoying. Shy/introvert/awkward guys don't have 3+ girls throwing themselves at him.
Having the 2 gay/lesbian couple in a group/school liking or love each other automatically as the only 2 in the area. In most comics stories it seems all same sex couples have to be is close to one another and BOOM, they date and fall in love. I get it that's the story, but it happens way to often to be normal. There are plenty of hetero people in group settings that don't date or actively hate each other in comics.
Finally I'm tired of basically the pursuer being all but a stalker/predator. This is a big trope in BL comics for sure. They get away with stuff no traditional romance could. It is a strange fantasy.
My thinking is make your romance as normal and realistic as you can while changing the setting. The situation can be different, but the people have to act like humans, not space aliens or how you think humans should act.