I agree with what he said, however, I think this situation is a bit harder. You and your girlfriend seem to currently have a pretty good relationship being able to work through all of your past mistakes (it's what makes a relationship stronger). From your post, it seems like your girlfriend is kind and understanding but she's also easily manipulated it seems. What happens if while she's there it escalates to "Do x for me or I'll kill myself" or "Have sex with me or I'll kill myself." It's terrible since it seems like he's just manipulating her but at the same time she probably feels like she can't say 'no' because no one ever wants that threat to come true.
I think there's more than just 2 outcomes and I think you hold a lot of power in this situation actually. What you can do is regularly check up on her by texting or facetime or whatever else (video chatting is probably the best option because then you can see her face). You'll still be giving her freedom but you'll also be involved in her life. Do this not to checkup on how they're doing but to checkup on how SHE'S doing. I think that's the best you can do since she clearly seems distressed from all of this and I think you can help her the most.
Lol this also turned out longer than I expected