oof,
So first of all, I would like to say , I'm not a pro in relations but writing your story down might make you feel better which is good. Your relations just like any relations, it's like a roller coaster and it's normal you can ask a lot of people and they also went through a lot of hardship during their relations. Some people were weak minded and decided to give up and look for someone better(?) and some people decided to stay in their relationship but suffered a lot. I think all those fights is what determines a relationship's strength. I think before proposing to her, you should have thought about your future with her and maybe questioned yourself on whether it will impact her life or not because you said she was young and I am assuming innocent but marriage also means restrictions. She is young and therefore she might take a different pathway or want to change air, have fun, be free of her own emotions maybe.
I personally, from my own point of view think that you need a serious break. A break from everyone. Start all over again, recreate those feelings you lost when being with her and the only way to do that is to rediscover yourself. Create new, healthy habits and first think about your mental health, that's the most important, you don't wanna hurt your loved ones.
By taking a break I mean, go outside the country, on vacation, or discover new hobbies... and she needs to understand that. All humans need their own space.
I would like to refer to your relationship like hair, right now I guess there is a lot of breakage and in order to repair that you need to start from the roots.
Don't stay away from your problem either because you are just going to make things worse but give yourself a break from your relationship just for one month and gradually make things up like go on a date for example. Don't go too quickly and make sure that it's gradual. rushing things will make you uncomfortable with her.
Hope this helps.