I have a friend who's SO behaves in a controlling and manipulative manner. The SO plays off my friend's low-ish self esteem. There is no single incident I can point to, but a large number of "little things". One of the bigger things involves bowing out of an event they were planning to attend at the last minute. I know my friend was excited and looking forward to this. It was pretty clear that skipping it was the SO's idea. This same thing has played out on a smaller scale many times with more minor activities.
The dynamic going on is kinda obvious to others who see them together, but, being in the middle of it, I doubt my friend has any idea.
Beyond what I've decribed, I'm not aware of any abuse or other misuse in their relationship. In fact, I was on friendly terms with the SO when they first hooked up, and still would be if this weren't going on. Although there is no formal friction between us, I don't feel comfortable hanging out with this person any more. I just feel that the manipluation is distinctly unhealthy.
Basically, I have this bad feeling that since my friend is a grown-up, I kinda have to bite my tounge and let this play out. What is the line between controlling behavior and abuse? I really want to step in and say something, but fear this will probably do more harm than good.