I am sorry to hear that, Islands, I think that LCM gave you some good advice. Some people are just born miserable and don't like to see others succeed in living to the fullest. Don't internalize the hurtful things that your mother says and persist in making your own path.
If she starts to threaten you again in order to grab your attention, remind her that it is Ramadan and she should be mindful of her akhlaq and speech towards you.
If she insists and keeps it up, don't get riled up or confront her; She's merely trying to control you and getting you all emotional to make her feel better about herself.
Instead show apathy to her when she criticizes or complain about you and your fiance. Apathy means that she no longer has no control over you. When she realizes that she is merely wasting her time in trying to upset you, insha'Allah, she will stop and rethink about how she treats you as an adult.
I know that my advice is probably going to be very controversial to some, but all of this is easier said than done.