So there is this girl who I met recently. Started off a little rough but got a lot better afterwards. The last time I saw her, she said "I'll be in town" and gave me her number. That was a week ago, and since then have had a couple of conversations but it has gone cold. However, this girl is already with someone, but seemed to be interested in me. How do I go about letting her know that I want to continue being friends (with the option of 'upgrading') and try not to steal her away from this guy?