Well, it depends on what you mean by "with"...
If one is an ex - that should be easy to cut ties with her - just be completely honest about it, odds are she knows how you feel anyway.
If one is dating your friend.... well - that's an easy out. You're not being much of a friend if you give her "that" time of day. She should understand.
The other girl is "new"? Just don't lead her on. From the little that I've read - you seem to be too nice for your own good. Just be polite and courteous around these girls without leading them on. Honesty is the best policy!
Good luck!
EDIT: I didn't read well enough - you don't want to get rid of ALL of them... I agree with Malevolent - the new girl is the best (IMO only) option you have to keep!