bestfriend in trouble what should she do?????

ok bestfriend has always loved being with women rather than men, she tried havin men hetrosexually but it never works out so she stuck to women on a permenant basic until recently.

she's now involve with a guy from work (for 5months)who happens to be married(wife out of town).

and for the first time in a long time she's physically n sexually attracted to a man.(which i think is good for her in someway) problem is now that her feelings for him is getting deeper she doesn't know what to do.

now he tells her he'll be leaving soon to join his wife out of town and assures her that what they have isn't only about sex but she thinks that she being used like in pass with other men. she has a girlfriend (for 2yrs) but isn't allowed to see her openly bcuz her mother doesn't approve of that lifestyle.

she's frustrated alot over her life bcuz she wants to be with her gf but mom won't allow it and he's committed to some1 else n she maybe in love with him. my advise is requied as her bestfriend.