I'm sure this gets asked alot, but I'm curious how to practice gaining self confidence and have "it"?

My girlfriend left me to get with another dude who looked like to me a "downgrade". Chubby, unkept, much older, etc. etc.

When I asked her what made him so attractive to her, she said he is masculine, knows his worth, and confident. Nothing gets to him and he has a beautiful personality that he is secure in. These are all things I lack.

How do I improve these things? How does one grow into the divine masculine and not second guess themself constantly? Many women have told me the most unattractive thing about me is how unsure of myself I am and my lack of confidence.

I don't want that fake macho confidence either. I want genuine self love and to make people gravitate towards me because of how secure I am in myself.