I feel if being his friend isn't detremental to your healing then go with your heart.
Remove the sex part from your post, add emotional, sometimes physical abuse +5yrs and you're living my life. I've tried everything to help my husband overcome his anger issues and now depression. He moved out, I begged him back. Then I realized it wasn't helping either of us. The nicer I am, the meaner he is. When I get angry due to his temper, he's nice and wins my graces. I love him more than anything and we were bestfriends for so many years. But I realize now that he must help himself for a change. I've done everything for him all this time, taken his crap because I knew his storm would pass and we'd be friends again. His recent storm has lasted 3 years and I can't do it anymore. But like you I can't turn my back on him completely. I told him I wanted a real seperation this time to give us both time to heal. I block his calls and text so he can't get in my heart everytime he feels like it. I call him everynight to say hello and see how he's doing. Now he always says " please call me tomorrow". Before it was "WTF? CALL ME NOW" so I'm hopeful he's working through some issues in my absence. The daily call is for me too because I suffer from seperation anxiety. I miss him terribly... until we spend time together. Then I realize I miss the man I married not the man he is now :-(