If you're in a bisexual female relationship and your girlfriend tells you she wants to try something new as far as messing around with someone else what should you do or feel?

Well, personally having been in this position, I think you should let the other person experience something new. If this person loves you they will be back. Obviously there are questions in her mind that need to be solved. There is nothing you can do to answer those questions, and being understanding will help the situation. She came to you with honesty, so obviously she really respects you and did not do this behind your back. This could also be a test from her just to see if you really care about her. Play it safe and talk thru this and maybe after all, she will decide not to do this! After all there is no touch or feel better than one that truly comes from Love. AND maybe this experience will prove this to her!