Excellent points to ponder What you feel and worry about are valid. I hope hearing that makes you feel better.

Is it possible your acquaintance is pulling back on account of you attending the group she leads? Could it be a case of her attempts to be professional? even if it is backfiring?

Does she treat everyone and react to everyone in a similar fashion or is this fellow getting his own undue attention.

Could she also be attempting to be nonpartisan for such reason she is a leader? This would be the professional thing to do. It is what I would do.

Thus, I wouldn't take this as her slighting you. From what you have said she is merely trying to treat everyone in the group as equals. Again, it is what I would do. In fact, when I have been in leadership positions in which some of my subordinates are friends or acquaintances it very much has affected the relationship. As their leader I need to remove from the situation of any appearance of favouritism. I take a step back from the friendship myself. My acquaintances had to deal with this.