I (18M) have been acting horribly to my partner (18NB). How do I fix it?

So lately I've been struggling with telling care of my partner the way a good boyfriend should. Whenever they've been telling about wanting body modifications I've been negative about it and very against it simply because it's not attracting to me. I've also been a bit distant and cold towards them. My partner has stated that if I don't fix it soon they will leave and that's absolutely not what I want. Please if someone could help in how I could change to be better for them I would appreciate it. However I am not waiting for replies saying they should leave me and find someone better. I want to become the better someone