What do you think of me telling my friend I don't think her boyfriend has good intentions?
What makes you think he doesn't have good intentions?
There's something wrong about his behavior, and I don't trust him.
It's not a good idea to tell your friend that you think her boyfriend has bad intentions, because getting inserting yourself into another person's relationship is a bad move. I think you should keep your opinion about her boyfriend to yourself, and let her decide on her own if he has bad intentions.
I'm going to say what I feel and how I see it.
If you get involved with your friend's relationship, it may cause your friend to think that you are just jealous. It's best to keep your opinion to yourself.