How to get rid of depression and suicidal thoughts?

Hello doctor,

I have had depression for over a year (at least symptoms of it), and suicidal thoughts almost as long. It was caused by a high school crush and has caused me to hate myself for everything I do because I am socially awkward and tend to mess everything up. I feel like I am a mess and that I made my crush life difficult at least at first, though memories are haunting me.I cry every day, the only reason I am not dead is that I do not have access to a gun. My question is about what happened today.

After school I saw my crush near who have missed the school, and she was with friends, when she saw me she came towards me and as is tradition in my country she kissed me on the cheek which was unexpected and caught me off guard, especially since we have been ignoring each other this whole school year.Whenever I have to interact with people I hate myself after it because I do not know what to say usually, and this case was not different either, but it was worse than that (because it happened in front of her). Anyway,

I left kind of awkwardly, and immediately I felt this unbearable stress, I wanted to shout but contained myself in public. Still, I made screaming faces, did that thing where I manually can create pressure inside my head and turn my face red like a tomato.I also sweat a lot, and I clenched my fists (not only), with which I would hit my other hand sometimes. It was like waves, I would feel super stressed at times, and then it would let off just a little. I could not hold back my tears. When I came home, I cried hating myself, looked in the mirror, and flipped off myself, told my reflection that I hated him, and I wished him to die so badly. I have never experienced something like this, at least not as strong as this. What happened to me, and how do I prevent it from happening ever again? Because it was awful.