I'm not sure I can offer much help. My "jealousy" tends to spikeover the day to day stuff, not sex. Sex has never made me feel threatened. But knowing that my husband is carving out time to console someone, plan fun activities .. day to day style things as examples -- those build relationships.
We've gotten throigh these by the somple expedient of talkong it through, his understanding, caring amd most important -- hearing my words as feelings that matter instead of hearing it as an accusation, that has been my key.
We have a rule now that i need to know his friends. What i didnt know is he wanted it that way the whole time.
She may benefit from having someone to talk to. Its hard when you feel you are differeft and no one will ever understand.
Until you two do decide what action to take, keep communication open is my best advice.
If Plan A fails, remember you have 25 letters left!