Accept that not everyone will like you back, in fact, most won’t. Mourne the loss, be sad, cry, then get up and carry on, because there will be another.
I also prefer to stay friends if I can, because if I loved them for some reason, them not feeling anything for me doesn’t change that, so I want them in my life.
Some of this was only possible due to the fact that I have had my heart broken too many times to count, so it’s also a thing of practicing radical acceptance.