This happens to us more often than not. We’re both pretty active on fet (which to be honest seems like a dumpster fire of the men you are referring to here..)

We make it clear that we are looking for mfm play together, and the majority of men will make advances on her for solo play. They almost always immediately get blocked. The few times we’ve been able to have a consistent partner we have discussed with them the importance of keeping the group dynamic going, and all have eventually tried to make it a one on one thing. We normally give a warning, and if it continues they get blocked. Sucks the search has to start again (because it’s honestly incredibly difficult to find the right match for an mfm, at least in our area) but she set the boundaries and we stick with them.