if he was your ex you should be over him. If your not over him you should tell your friend or try to get him back.
Tell your friend that you dont want to see the friend of a friend as you would like to spend some time with your ex, i am sure he will understand.
You can tell if he's flirting with his ex, and texting/messaging her. If he talks about he sometimes as well.
get over it
I would tell my friend to be cautious about going out with my ex.
you should try telling them how you feel or go over to your ex boyfriend and ask him if he likes your best friend THEN you might want to tell them how you feel depending on the answer.
'Ex' means that relationship is over and there is no need to tell your ex boyfriend you are a lesbian. However, if you want an honest friendship with your friend then time some private time out for the two of you and let them know just who you are. If they are a good friend they will stick by your side and if they don't then they were never your friend in the first place.
if they are really silent when there by or talks to him alot or flirts with them
You tell her how much it hurts when she, talks to her ex and if she loved you she would respect what you said and stop .
Tell him firmly to stop texting you, and ignore him if he continues. Be polite when he talks to you but have lots of excuses ready to cut the conversation short.
You can tell your friend that you have some feelings and not to be all kissing in front of you or I like you more things.
She just might want to be your friend still or is not completely over you yet and does not want to let you go.