I've never been through it myself in terms of a romantic relationship.
I suppose that would hurt quite a bit when you're trying to convince someone that you'd never jump to some other person but they refuse to believe your a kind and loyal partner even though you've never cheated or had interest in someone else. Packs quite a punch.
Seriously, uke pisses me off. He treats his boyfriend badly. Then he runs away and cries and insists on thinking that it's okay to keep running away and his boyfriend will come to him every time and forgive him for everything. He just takes everything for granted. Satoi should just dump his ass and date Mifune instead. He's kind and considerate and will actually treat him well.
The uke really needs some reality check. I get that he's a loner and everything but his pessimism is really annoying. It hurts to think that your lover might be snatched by someone else but it actually hurts more when you tried hard to show your lover love but he actually thinks that you'll just jump to another guy that's willing.