Staying friends just prolongs the agony. Understandably, it is hard to let go but staying friends seems like she's stringing both of you along and just keeping her options open.
Give yourself some time to heal, if you can't bring yourself to delete her number then at least remove it from your phone…put it on a note and file it somewhere. If in a few months (or so) time you feel you can handle 'friends' then contact her to see how she is….never look back!
The fact is that trust is long gone and even if she came back I could more or less guarantee it wouldn't be for long.
Some very good advice in previous posts…..have another read and reap the experiences of others.
Good luck fella