You feel disappointed because:
1. you have expecations for the things you have done for your friend, and
2. you assume your friend knows your expectations all along, and
3. your friend did not meet the expectations that you set for yourself.
A clever woman as you are, I think you can immediately tell what is wrong in this logic.
I think there is a difference between lack of appreciation and lack of ability in expressing the appreciation, bearing in mind not everybody has a good social skill. From what you said that your friend also introduced their friends to you and stay in your place, it seems at least that your friend trusts you, and might have said some good things about you to their friends too.
If I were in your position, I would ask myself whether they have caused great inconvenience to me in the past? if not, I would let it go. If yes, I would explain to them nicely next time round that things have changed since your marriage and you have other engagements to consider.
Afterall, your relationship with this friend is perhaps "inconvenient" rather than "toxic", and does not worth the bother in my view. Think about it, you may create an enemy for yourself unnecessarily by sending a "termination" letter :)