Okay so if you feel like you can relate to this one-shot, like I somewhat do even though I have never really "liked/loved" anyone (maybe ace + issues lol).

Most of the reasoning here is absolute bullshit, and kind of disgusting if you are actually saying it to others (here it is sad since the MC seems to be reproaching himself).

Firstly, it is normal to want to change, in fact if you are willing to try and change you are likely better than most people as you show you are able to acknowledge and want to change and it is not disgusting as the girl in MC's dream portrays him to be.

Do not guilt yourself into thinking that aiming for a better/happier life for yourself is selfish.

As long as you aren't actively depriving others to a SIGNIFICANT degree of course - any action/inaction will affect others so in some sense you will just have to ignore it. In fact most people already do.

To some level, everyone should be able to be self-serving and that is okay, and should be differentiated from being selfish. (God I wish I could actually feel this instead of logically understanding it though)