Most likely because he dated people who came his way and he never truly loved them. People would realize that soon enough and dump him afterwards. It was different with Ryuusei because he loved Ryuusei and didn't want to lose him so he put in the effort to not lose Ryuusei.
He's really so strong for keeping his head high and doing the rational thing. If that was me and I saw my mom in that situation, I don't know what I'll do. I'll probably tell her the truth and give her two options...or maybe oblivion is bliss. I can't. This is too much heartache :(
Please update this (/TДT)/