Your FMIL sounds amazing. And so do you! Good on you for standing up for yourself with your fiancé.

His behaviour in all of this isn't okay. Even if it's a matter of being stuck in the middle with a long time friend and your partner, he should never have been so dismissive of your feelings but to be frank, he should have stood up for you and shut her down immediately. That's all there is to it. Especially considering the things that she was saying. Because if the situation were reversed, I doubt you would be so dismissive of his feelings. Even still, the fact that he hasn't contacted you is far worse. You had a fight... Yeah it seems like a bad one but really? His response is to sulk and cut out his fiancé and his mother for a few days? This is the man you're going to marry. What happens when he's your husband and you get in another big fight which... let's be honest you will. That's just inevitable when you're committing to another human being for the rest of your life. What happens when you get married and his little friend is rude to you again? I think these are definitely things you need to sort out before you get married. What he said to you was out of line and how he's acting now doesn't inspire much hope in his ability to stand up for his fiancé/wife or his ability to deal with conflict like a grown up.

As for his friend, you could try to give her the benefit of the doubt and say maybe she was intimidated and she's awkward and gets nervous and explodes in word vomit but you know what? She's a grown ass woman and really, she should know comments like that are out of line. She's insecure, probably jealous and intimidated by you and maybe wants your guy. She sounds like a child playing at being an adult by what you've said so take it as just that. Besides its your fiancé's job to place boundaries and put her in her place if she disrespects you again.

Hope you can sort it out OP but still super impressed at how you handled yourself.