There are obviously two issues here; his sobriety, and his relationships.

What is happening with his girlfriend is abusive. What is the nature of your own relationship with her? Are you good friends? Are you able to discuss this with her? A good way to initiate a conversation is with the "I have noticed that..." What do others around her say and feel? Is it possible to hold an intervention for her, demanding she get her own help for herself? You might encourage her to attend an AlAnon meeting.

As for your friend, he may need an intervention himself. Perhaps though you can start with smaller steps. Offer to attend an AA or NA meeting with him. As for AlAnon meetings, I recommend you attend one yourself. They can offer up encouragement and resources for how to deal with such matters - and not forget yourself in the process. [While AlAnon is for family and friends of alcoholics many groups welcome those people whose lies are affected any addicted loved ones]