How to avoid dating an abusive creep
One thing that will help you is to focus on what you can do, rather than on what you can't.
However, my roommate/close friend started dating him four months ago. Knowing about this guy's general creepiness and having seen this friend disappear almost completely from our social circle to spend all her free time alone with him makes me worry he is abusing/manipulating/being an asshole to her.
When it comes to heading off her bringing him along to these meet-ups, there are a couple of approaches you could use.
One is to make it clear that you want it to be just you and her who hang out.
But she isn't, or she's choosing to read them as something else right now, and trying to force her to see what you see will make her pull away from you. You can keep in contact with her, be that through social media, email, texting, whatever you like.
Try to keep the conversations between you as normal as you can, to avoid making her relationship with creepy dude the focus of your time together.
Praise yourself for accomplishments, little or big, and counter any negative self-talk with positive mantras or affirmations. Recovery looks different for everyone, and each person has to find what works for them.