I think my weight and appearance is ruining a relationship
Do you think that the way you look if affecting your relationship with your partner?
Yes. I am not able to wear the fashion my girlfriend likes
I would hope she likes more things about you than just your looks and the clothes you wear. That being said, physical attraction is a part of relationships and some people make it a priority.
I just want to wear cute clothes.
I'm sorry you are in this situation. People shouldn't based their feelings solely on looks. Sometimes people don't want to be in relationships if their partner isn't attractive, but  if this relationship is making you feel bad, you could end it.