Only if you don't mind hurting both of them by tearing their friendship apart.
It will probably cause a lot of trouble...
Yea for sure, but first talk to the girl you like about how she feels about the situation. Speaking from a girls point of view this is usually a really tough situation
What took ya so long?
Your ex is your ex-it's like once you sell something to someone it is sold-unless of course you still want the ex.