Thank you for letting us in. I'm sorry to hear that, I can sort of relate because I sometimes go head to head on certain things with my parents (mostly my mom), my dad is always neutral.. but just keep a level head through out all of it. I know most things are a lot easier said than done, but as rough conversations come up then try to keep your patience because it will make you a better person for it, and eventually you will learn to not let these things get to you anymore. Take the example from your fiance. :)
He sounds like a great person and if you are saying so then you shouldn't doubt the decision, since after all, your parents approved of him themselves in the first place, its not like you are going against them. Now if they are having issues with him being in your life, I mean I don't know what to say to that, I would never want to disrespect anybody on here by saying the wrong thing but maybe you should try talking to them? You are independent and old enough to make any of your decisions by now and go about them as you see fit and if you are marrying this person, then your family may also need to understand that he will have just as much of a say, in your life, if not more after the wedding.
I mean as long as you are still "under their roof" (not ruksat'ed) then try and keep things balanced with them up until the wedding for the sake of things going smoothly and not trying to get anyone upset. I can see you care for both your fiance and your family both but it is up to you to create the balance if problems are arising.
I mean once your married and living on your own, how much will your parents be able to keep you dependent on them. You will start to settle in your own life with a new partner having to make personal adjustments of your own and they should understand that but if they don't, that okay, just approach it to their understanding. It can be tough between families and your significant other for sure, but just be patient like the hubby to be, and support each other, all the mean while supporting your parents. I think the most important thing would be to try and keep the respect between them both, in both his eyes of them and theirs of him...I think that will go a very very long way. Otherwise, there will always be some kind of blame coming from one of them towards the other, only making it harder for you to keep things grounded. So same advice as before, try not to let them in to much about your fiance because the more they know, the more that may go against you in the future.
Inshallah your parents will come to understand what you want them too and it all settles down once the wedding is over. :) But if your telling me your fiance is an amazing person with and to you and you care for him very much, then I don't think you have anything to worry about because good men are few and far between, and you have one of them to spend the rest of your life with. :) I think that decision in your situation is the very LEAST that should worry you. :)
I hope that helps you out a little bit. :)