Unsupportive "Support" System

Sometimes I think my friends don't really like me that much. I'm always seeing pictures and updates on Facebook where a group of nearby friends is going to the movies or eating out or going to sporting events together, and I notice how I wasn't invited.

There's a group of friends meeting at the church tomorrow to help set-up for a meal after service. I told them I could help, and to just let me know when they were meeting. About half an hour ago, I sent a message via the Facebook group chat, asking if plans were made and if they wanted any help. Evidently, they had all already decided on a time to meet and had delegated tasks and everything. They were quick to say that I was welcome to be there if I wanted, but they had everything under control.

Right now, there's a group of four young women, all within two years of my age, seeing a movie at a theater not even 6 miles from my house. They know I've been feeling isolated lately and that I am trying to become more socially engaged. I don't think I've done anything to offend any of them. I'm assuming they just didn't think to invite me.

But how is that supposed to make me feel? These are people I see probably once a week or so, and I interact with on social media fairly frequently. I guess I'm just not that important to them. When I do get invited to things, is it always an afterthought? Do they ever look forward to my presence in the same manner that they look forward to seeing other friends? Do they think of me as more of an acquaintance? Because, they are at the center of my [limited] social life, and I kind of count on them for support. Things like this happen, and then I'm left wondering, "Would anybody notice if I was gone?" When I'm dealing with thoughts of self-harm and suicide, I try and think about how it would devastate my friends and family. But maybe I overestimated my impact on them. Maybe they would hardly notice at all? Next time these thoughts and emotions creep in (and, believe me, they will), what's to keep me from acting on them? Thinking of my "friends," who never even think to invite me along? Would they be there for me if I really needed to talk or if I needed help getting to the hospital, or would it be too much of an inconvenience to waste time and effort on a mere acquaintance like me?

I'm feeling pretty worthless right now. And burdensome. And alone. What do I do from here? I can't just fabricate new friends out of the ether. I can't just somehow instantly make relationships stronger, especially when they weren't nearly as strong as I thought in the first place. These things take time, and I think I'll have that kind of time before the next mental health crisis strikes. Part of me wants to just give up and give in to the little voice in my head that tells me to kill myself. No more guesses. No more social spider webs. To just be Done.