Accept she wants the relationship to change.
Block her on social media.
Don’t allow yourself to do any online stalking
Delete her number
Delete all messages
Block her number
Dont find a way to unblock her or restore the messages
Dont try and be friends. You sound too far in deep for her and honestly, if she can be, it wasn’t deep for her or she is building up your hopes of friendship without really meaning it.
It will be tough.
Find something else to do with your time.
If you have a group of guy mates, go out with them, if not, join one of the organised kind such as Masons or Rotary and get yourself some not female friendships going where they will empathise, understand, and buy you a pint and then talk about something else with you.
Dont feel sorry for yourself. The next girl won’t find you attractive for it. Ultimately, it’s her loss. You sound like you treated her decently, a few mins on here and you will see how many male idiots there are. Get yourself down to the gym.
Don’t try dating for a while - i suspect it will take a few months for you to get over her, and if you get out there desperately looking to replace her, you’ll come across as desperate and needy. Just break the cycle.
We guys can fall deep and hard, in these situations, somehow girls just seem to be able to brush us off easily, probably because they have more choices, not usualky better ones though. But tastes differ and i’m sure in time if you look after you, prevent her from playing games with you and your feelings now, find something else to do, and yes it’s ok to lament what you’ve lost, but put it in perspective, there’s 5 billion more fish in the sea.
Don’t be a stalker. Do let her move on too.
And good luck. It’ll be tough, but you will get past this.