Hey Guys, plss i need your candid advice on what to do in a situation like this.

I'm a single guy, though searching. There is this girl that my friend introduced to me as his new catch (you knw guys like that). So i started treating dis gal as my frnd fiance (though i knew she's only a side-chick to my guy). As times goes on, after many moments of talking, playing, gisting and sharing d past happenings with dis gal, i found out dat dis gal has some kind of feelings for me (in love) , i can see it in her eyes whenever we're talking, but am not carried away by it, i still mentain the fact that she's my frnd fiance.. Even d gal prefer spending more time with me whenever she comes, than with my frnd.
Towards d end of last year (Dec),, my guy had a fallout with this gal bcos she won't let him IN (hummm!).. I tried to settle it but d gal told me she will never allow my frnd IN and asked me if she's my sister, will i advice her to do such?! During d course of our conversation on dat day, she told me 'she wish i was the one in her life' and not my friend (she finally told me her mind)... Since then, their relationshp has not being d same. The problem now is dat dis gal doesn't want to be in relationship with my frnd anymore bcos he realise d kind of guy he is. She now wants me! How is dat possible you say? Yes she wants me, she told me some things about herself that i dnt believe a gal should be telling any guy, even her fiance..
I don't know what to do, this gal really love me and i know it.. Am thinking about how my frnd would feel, i knw he would feel bad cos any guy would..
She doesn't even care if am a JAMBite, she's in 200L level with my guy..