<human>: Can you condense the text into a few key points?

So this is my first real serious relationship with this girl (3 months, not too long I know but serious for me). I like her and I'm sure she really likes me but there is this one thing. She seems to keep in touch with a lot of ex boyfriends as friends. Now I've said I trust her and she's been cheated on before so I'd hope she wouldn't do the same but this one guy in particular, who apparently was in love with her, seems to be talking to her more and more. Initially he hated her because he thought she cheated on him with me (which isnt true they broke off long before). But now they are talking again. I'm not entirely sure what they are saying and she says its just about weed connections. She's done other drugs with him when they were dating and he offered her some the other night. I was really uncomfortable because I do not endorse that at all (weed is fine but coke is another thing). He sounds like a real bad person(ie. putting MDMA in her drink when she wasnt looking, but she saw that the drink looked funny so didnt take it), and she's even admitted he is a dick. My main concern is that if she hangs out with him she will either get into drugs (intentionally or unintentionally) or he may have this feeling of revenge for what he thinks she did and she may get hurt. Anyhow I'm not sure what I should do to tell her. She knows how I feel and I do trust her but, like I said it's my first real relationship and these feelings are new.
<bot>: Girlfriend of 3 months is talking to ex boyfriend drug dealer who she apparently hates but sometimes says he is nice. He's done some questionable things.