The ex guy is the embodiment of someone who fuck up in life and desperately wants to repair what he previously had, selflessly. He doesn't even try to understand the feelings of his ex, or more like he doesn't care about them anyway. He was a selfish asshole when he left and he is still one now that he returned. He is so insecure, he has to resort to insulting his rival (MC) with stupid things like him being a virgin. And lastly, he put an ultimatum on MFC proposing her, WHO DOES THAT? A selfish bastard that's who. he wants to fill the void of his failure by reviving the only relationship that meant something in his life. I see a lot of people complaining about this arc but keep in mind that people like this really exist in life, author-san is just helping us to recognize them with and obviously a version of a character.