What should you do?
The wise thing would be to stop hanging out with her with a view to moving on. Staying in this no-mans land of loving someone who doesn't love you in return isn't how to look after yourself. Yes, I realise you will miss her - but it will fade in time.
Yes, she will probably be upset about losing your friendship. So tell her that you're sure she understands that if you can't be her boyfriend, then you need to move on and forget her.
Never regret anything that has happened in your life. It cannot be changed, forgotten or undone. So, take it as a lesson learned and move on.