My sister got married maybe a decade ago. Now most of her friends are married as well. I think I am one of maybe three of her single girl friends (and I am not sure I count). I am not sure if it’s true with everyone but from what I have seen married people tend to hang with other married people. So when the marriage falls apart - One way or the other it really is hard to start again because most of your friends were your friends of the unit and not the individual.
In Jen’s case I can see how a lot of the people she spent time with with her husband just don’t know how to approach the single version of her. Which only fans the resentment she is feeling. I can see the use for the support group in just that it introduces her to single people.