How do i tell my boyfriend his friend is not good for him?

Ok I have a ques for people mostly in 30s. My boyfriend ,33, just reconnected with an old friend. He ran into him and my boyfriend misses his friendship. Reason they drifted is because his friend kind of abandoned him when he was going through tough times. Also he was type who wanted to be single cuz he was huirt by woman and wanted to see my boyfriend miserable and alone. So he would try to say things behind his back to his girllfriends and start trouble. I am really concerned that friendship will not be any good for my bfriend but i dont want to seem jealous or not supportive cuz he was happy they got closure. What could I say to him that sounds really smart in that Im concerned that friendship will bring him down and it wont be any good for him. Am going to send this to him in email and want to let him know I'm concerned but its up to him to make choice if he wants to keep friendship. please advise on some wise things to say to him & good points to make. Best answer 10 points.