It is dis-respectful of your friend to text your ex-boyfriend. It is common courtesy for a friend to ask if thats cool with you or not. Be nice back. Everyone deserves to be respected (unless proven otherwise) Also, everyone deserves a 2nd chance. Most likely your friend hasnt been taught about respect and courtesy. You can be a cool friend and teach her this by BRIEFLY talking to her(if you agree with this.) With her new knowlage she can prove her loyalty, and respect to you, or if she doesn't, you now know better, and can move on. Good Luck Sugar,
                                 CoCoCoMom

It could be possible that no that you two are no longer a couple, your boyfriend is moving on and his first choice is your best friend. I have seen this often in my experience with friends and dating. It does hurt to have your best friend even thinking about dating your ex, but on the other hand you have to remember that you two are no longer a couple and he has the freedom to date whom ever he chooses, which as much as it sucks could possibly be your best friend.

The best thing you could do is maybe sit down and talk with the two of them and find a way to express that it hurts you to see them forming a relationship and let them know that you are willing to respect their freedom to do so. Really the best thing is to let them know how you feel, but try and see their side of things as well