Originally Posted by SchrodingersCat
This is true, but that does not mean you cannot use your influence with him to voice your objection to the matter and encourage him to seek a different, less clingy partner. That doesn't mean you're controlling him or anything, he'll still make his own choice, but sometimes it's the responsibility of loved ones to tell us when we're being careless, if we don't catch it ourselves.
Yes, I see what you mean. I have voiced my concerns. It sounds odd in the context of bdsm but we have a sort of 'do no harm' agreement. By that I mean not getting involved with people who are vulnerable and not knowingly using/doing emotional harm to people. J is someone that he has been friends with for several years (mostly online). She has other partners, but she is not attached in the sense of being married or in a committed relationship. I think she is vulnerable anyway, but one of her partners has recently died. My first husband died (in very different circumstances) and I know that a close loss like that can leave you vulnerable for for many months or even years afterwards.
I may make one more attempt to advise caution and to point out the possible problems. After that I have to accept that they are both adults and if it is still what he/they both want I will not stand in their way.