She has been in the most ridiculous and dramatic relationship for about 2 years now, on and off. She lives 3 hours away from her family, though has a few good friends where she currently lives and her sister and her partner. Her and her family are not particular close, so tbh myself and her other best friend are the closest people she has. We really, really want to help her.
Over the 2 years there have been mistakes on both parts. He is a habitual liar, will take drugs, he also this ability to twist everything and make it her fault, make her feel guilty. She's ended it many times but after a day or two and some ridiculous 'ill change' speech she takes him back and the cycle starts again.
She however, when drunk will snog other men, will talk to exs (text, email). In October this built up and she slept with someone else. She confessed to her bf 7 days ago. He dumped her.
However Monday he came over to talk, ask questions - they ended up sleeping together. New Year's Eve she spent with her flat mate and some other friends, he constantly messaged her checking up on her. She hated this. As the day has gone on though she is now talking of missing him, wanting him back. He is messaging her again about how he loves her but doesn't know if he can forgive her. We think he will, and she will take him back because she feels like she should because she made this mistake.
It's basically a train wreck, we (my other friend and I) can just see the cycle repeating itself again, and it keeps getting worse! She openly admits she doesn't want to marry or have children with him, they don't even live together or have any intention of doing this. We are desperate for her to see that this is unhealthy, her confidence is rock bottom. We have made more last minute trips to see her after they've split again than I can count.
How can we help her? I know she did wrong, but she is my friend and I'm always going to side with her and want to support her. I just am out of ideas of how to get her to see that this is not how a relationship should be, before something happens like he proposes or she gets pregnant - and it all becomes even worse!