If she is really worried about diseases she should be insisting that he wears a condom with her rather than insisting that he wear a condom with others. We are all responsible for our own sexual health. I'm not saying that he shouldn't wear a condom with you (honestly until you've had that follow up testing 6 months since the last outside sexual contact for any of you there is no way to know that you're 100% in the clear). I would have follow up testing done (and ask him to do the same). Then you can approach this conversation with her again. Also try the female condom, it might be more satisfying than you think it's going to be.
Everything will be ok in the end. If it's not ok it's not the end.