I feel pathetic, worthless and lonely for about 3 months now

I feel excluded, resentful, bitter, sad, angry, suicidal and hundreds of negative emotions on a daily basis since about 3 months. I get so Angry and Sad when my friend do stuff without me. I doubt nearly every friendship i have on a daily basis. There are a few friends with whom i can talk about this and i ask them if we are still friends, they always say yes, they always say they'll invite me more and in the end nothing happens. I cant even discribe how incredibly wronged i feel.

In addition to that im feeling so lost and sad and pathetic because i would give a kingdom for a loving Relationship. I don't know why but do everything and nothing works and that just destroyes me. I know im pretty young at 18 years old but i don't know what will happen considering my current life. I'm asking for any type of helpful advice and thx for reading :) PS: im not a native English and super Depressed right now so sorry if you cant even understand what i wrote.