You'll probably have to accept it. Just voice your concerns and if you're concerned, keep an eye on things.
I don't know that you should necessarily believe "every single thing" that any one says, let alone an ex.
You should talk with your best friend. If you are really best friend you wont let this guy get in between you two. Yes, that's the right thing to do. In fact, after you talk, tell him that he'll have to take you both at the same time. Why not have some fun at his expense.
He (she) misses you
He really hates you
She just might want to be your friend still or is not completely over you yet and does not want to let you go.
Again, it is much easier to read and respond to questions that spell things correctly. On to your question, your ex's friend is only being loyal and supportive of your ex. You shouldn't be concentrating on him. It's your friend who should be more sensative to both your and your ex's feelings, yet your ex and your friend should be less careless. Maybe, if you are fine that you've broken up they think it's okay. But yes, it is wrong that he and your friend are dating so quickly. They are being selfish and senseless, and I suggest talking to both of them. Your ex's friend has done no harm.
Let them be happy and stop stalking them.
just tell your best friend that you really like him and see what she says about it.
Stay out of it, it's none of your business
that you guys can still hang out and there wont be any feelings for each other.
Well, the answer is clear... ask your friend if she's ok with you two dating. If she says yes then go for it. But of she says no, then the answer is no
well if you dont like them then let them be aloneee. (: