Dude. You are seriously over analysing.

What do you mean about "managing feelings". WHAT?
What is to manage?

Your ex. Is your ex. For one (or many) reasons. Potentially your fault. Learn from it, but don't dwell.

New girl. You like her. She liked you. You obviously didn't show enough investment to suit her needs. Take from it what you will. Learn from it. Move on.

Why don't you just ASK her?

Stop blaming yourself for everything, women are complex. The more you try to understand them, the harder it becomes. Just focus on yourself and let things fall into place.

Also look at the diagram I posted somewhere else: