After rewriting this several times here is the short version:

I have an okay life, I have a house, partner, okay job, hobbies, but I just want to die, I won't do anything stupid, I know it would devastate my family. I would probably be too afraid to do it anyways. My problems aren't severe, many people have much bigger issues to deal with. I often contemplate the future and always get to the same conclusion, it would be so much better without me. I keep lying to my family about my mental health. I'm always acting that everything is alright, lately, I started lying to my partner about many things, just to avoid dealing with him. We are engaged but I don't know if I want to go through with it or not. I'm worried that it will be just worse and worse. But I also don't want to sacrifice the last 6+ years. Then I start thinking about the breakup, then start thinking about how everything he does makes me angry, sad and hate myself. Then I'm back to that thought of how perfect would be just dying. I know I'm a coward. I know that when my partner makes me want to die, it's probably not a good relationship. But he can be incredibly loving and caring, with so many great qualities. It's just a rollercoaster for me. Lately, I just don't want to do anything. Almost every hobby I have got ruined. I'm almost incapable of having fun. Even sex is something I do out of necessity to appear normal. I sometimes feel okay when I'm alone, for a brief moment before I start thinking. I feel like the worst person, I know I'm selfish and want to die just so I don't have to deal with my problems. And it probably sounds really stupid, and maybe I am. But I don't know what to do and how to deal with this. Feel a bit pathetic even writing this. 

Sorry for wasting your time.