[Following up on this]

Endorsed contributor, /u/youllknowwhenitstime, coupled (independently, I think) with my husband, Z (45/m), solved the problem.

I mentioned to Z that I was getting concerned about L (38/f). Z immediately pulled up his Facebook messenger thread with her. She was complaining about her husband, J (44/m). Z had one line he kept responding with, namely, "seek a professional, and one whose specialty is not like mine".

Even when she observed that our daughter (5/f) is "beautiful because her father (Z) is handsome", it hasn't seemed to register with him that this girl is flirting.

Z: no child isn't beautiful, in my estimation... some stay beautiful -- [my name] and your good self -- others bask in your respective sunshine's, wondering how they were so lucky to grab the attention of such wonderful people. like me <g>

I love him and am so ashamed that my jealousy got the better of me.