Should I do this or just leave it be? help?

Im thinkin about datin this girl I met recently an I dont think it would be to hard since she obviously has a thing for me an I do like her a as a friend now, but as I get to know her more im likin her more. My problem is that since late june iv been talkin with another girl an flirting a little, she just deciced she'd rather we be friends an thats fine, but this other girl is curious about what happened. She doesnt know anything except that I was feeling down last week an my friends were talking about it a little, but she doesnt know what it was all about. Should I tell her how I was flriting with another girl for the past few weeks including the time when I knew she liked me? On one hand I feel like I should tell her since I want to start on a clean slate, but i also think that this would be really awkward to tell her an it wouldnt go over to well. we were chattin on fb today an she asked if the problem was solved (last week she asked what was wrong an I said I didnt think it would be a good idea to tell her until monday when stuff was sorted out) an I said still confusing, it would be awkward to tell her, an she said that whatever it was wouldnt be awkward but i didnt have to tell her if I didnt want to. If i do tell her Im guessin it'd be better to tell her in person?