Your friend's approach worked in my situation and brought H back home. Unfortunately, neither of us were healthy enough to work constructively on the R. I didnt issue an ultimatum, but did make it clear that I was moving on and he needed to make a decision and stick with it. Dr. Dobson wrote a book "Love Must Be Tough" and it might be a good reference for you. He talks about setting boundaries and making it clear that while we love our S, we won't succumb to be treated poorly. It's a matter of self respect. How can you respect someone who allows you to abuse them? He also says a lot about how to love and not chasing/pursuing our S because that pushes them away. Kinda like DB, except he strongly suggests that there is a limit to what we should take, and it's important that we set limits and protect ourself.
Sometimes the hardest part is the decision. I know that's been the case for me. When I was wallowing in confusion not knowing whether I could try again with H it was difficult to see which way to go. Either way I turned, I could see the obstacles and the pain ahead. Once I made the decision it was easier to accept walking in to the pain and doing the work because I had embraced my decision. Your H has no idea where he's going to end up. Are you allowing his indecision to keep you on an unknown path also? What does Hope want?