I like the term "distancing", although it doesn't do much to make it not hurt.
Someone very important to me said a long time ago that if we ever "broke up", we'd just stop having sex. When his wife started having jealousy issues and they seemed to need to work on their relationship, I offered to take a break from having sex with him, hoping they'd work through it and maybe it'd help build a foundation for a more solid poly relationship, not just FWB/dirty little secret. Then I waited, and we did a lot of talking, and I'm pretty sure that she is never going to be okay with me having sex with him again, at least I can't see it happening in a context where it would be an emotionally healthy choice for me. However, even though we're "broken up" and it was never an official Relationship to begin with, we're still really close, and I'm getting to the point where I feel like I need some space if I'm going to have the time and emotional energy I need to nurture relationships that could develop into the kind of poly Relationship I want...but no matter what I'll always be there for them when they need me, and I don't want to hurt either of them.