Sounds like Felix isn’t the only manipulator in the situation. You shouldn’t intervene, girls don’t like to feel controlled, nor do they like for guys to keep trying to pursue something with them after they’ve said no. Let her make her own choices. Try to figure out if your dislike of Felix is coming from real concern or jealousy. If he’s really a bad guy, hopefully she will break up with him, but your opinion on the relationship will probably just make her annoyed with you at this point. Talk to her friends to try to see how they feel about Felix, if they also think he’s a dick they can talk to her themselves. Do some self-reflection and change your attitude if you ever want a chance. Otherwise you’re just as bad as him.