Hi Scrubs,
Just off the top of my head, it seems to me you have too many negative thoughts, both about yourself and other people, that are causing you to not like the other people (fiance's family) and to think other people are judging you negatively.
These negative thoughts can be caused by fearfulness, and also anger, also grandiosity. You might want to focus your mind on this: we are all human beings, none of us are "perfect." No matter how old we get, we all have shortcomings. And we all need love, acceptance, and approval from each other. We all laugh, cry, sweat, and poop! We are every one human. And we need each other to fully live and be happy. So take a breath, and just detach from those negative thoughts about others and yourself. Rememeber none of us is perfect. We are all human and vulnerable. Work on accepting yourself just as you are, loving yourself as you are, and if you're able to do this, it should follow naturally you will be able to better tolerate others.
The other thing is you seem to feel insecure about yourself, so you feel resentful/jealous of your fiance doing things without you. It might help you with this to consider this: every human is unique. The relationship your fiance has with you, is completely unique. He can't experience that with any other person. Your relationship with him is completely unique. What he feels and experiences with you, he can't duplicate with any other person. So what you offer him, as yourself, is uniquely of value, just to you.
The other thing for you to understand, is that humans need relationships. Through relationships we learn, grow. Relationships enrich who we are as people. They "fill us up," emotionally, mentally. Your fiance, and every person, needs relationships, and the richer their relationships, the happier and healthier the person will be. Think of his other relationships as "drinking from the well," and they enrich him as a person in various ways. These relationships also can feed your relationship. You can't reasonably "keep him all to yourself," because he will "shrivel up," so to speak, like a fruit drying in the sun...he needs nurturing to be strong, and he can't get all he needs from only one person.
I wish you well! Maybe this will help! Wisdom I've gleaned through much suffering and learning!

And when it comes to stress and upset, remember to breathe, it helps!