Michael, your last message made me smile. In your original post, it struck me how much you assumed control over how this relationship played out:

“As things have got more serious and we’ve ended up in a relationship after much ‘wooing’ on my part, surprise trips, romantic dinners, I wanted to show her that she was special and that she didn’t have to be the person always giving in a relationship, as had been the case for her previously.”
“My first feeling was not being good enough, feeling like I should’ve given more or myself and tried harder.”

Sounds to me like you tried very hard, and yet you tell yourself you should have tried harder. “If only I’d done it right, I could have made this relationship work!” As if you are the only person in this relationship. As if relationships are a videogame you can win if you’re good enough and know where the ammo pickups are.

You did what you could, man. And you’re still doing the right thing now, by giving her space. Cut yourself some slack and just allow yourself to grieve a little for what could have been, rather than trying to figure out how this could have been prevented.

All my best wishes.