This series is one of those "good premise, bad execution" types. Every character is extremely one-dimensional, except the abusive ex-gf, who is only somewhat more interesting. The setup was there, but the author didn't really know how to make the characters feel believable enough to make it work.
The MC is a blank slate of a man that doesn't even get a bonus to personality from trauma, since he seems to have almost completely gotten over his abuse with no lasting effects on his character or psyche. He's just like, a dude, full-stop, nothing else going on. I get that it can take time to find yourself after escaping a relationship like this but it is not framed as him still finding himself, he's just another self-insertable nothing-burger person with his only real trait being "vague kindness". The FMC is just the "meek bookish girl with glasses" archetype with no real personality beyond liking the MC... idk, it could have been good but it's just not written well enough.