It's good that you are being a pillar of support to your friend. Be careful to not get to caught up in the monitoring of his cycles and patterns.

As for the girlfriend, it's up to her to decide in her own mind when she has had enough. I can actually relate to her story where my exh who is without a doubt battling addiction, er, um not sure if it's really a battle more like living the life--he beyond a shadow of a doubt had himself convinced that I must have. The marriage disintegrated from that point forward. It took me a couple of years, a couple attempts to leave and some generousity of family to help with the legal retainer. Just know it takes time to feel at peace with the decision before what felt like jumping off a cliff solo with kids and a society that at face value cannot comprehend.