You should never have to apologize for any of this.
You are not alone, and honestly a lot of what you have written, could have been written by me.
It can better. It does.
Having Anxiety and other such issues Sucks. I know it all to well. I battle my "Demon" as I call it every day. Some Days I win...Some days its a draw.
You aren't alone and there are actually people out there who do care, and do like you, no matter how you feel and what you feel you present to the world.
You are not alone. Don't be afraid to reach out.

This is going to be a long post to your long journal, sorry in advance. Just know that I'm a survivor of eight years of urban violence, I've had PTSD and suicidal depression. Complete with attempted suicide and episodes where I was forced to relive the same horrible moment of my childhood where I got nearly beaten to death and survived eight years of urban violence. I've literally had to fight for my life more than a combat veteran who serves two to four years in a warzone but will never get any sort of respect or admiration for it like they do. So know that I'm not just some schmuck on the internet giving advice. I want to help, and I know how bad it is when you've got depression and PTSD wailing on you.
If anyone is telling you to "cheer up" or that you're "using your depression as a shield", that's pretty awful. It's sad to think that some people actually do try to hide behind supposed depression, I've seen it. But if you've got depression and someone's telling you that, you may need to find a new group, or tell them off. It won't be easy, but you may need to sternly tell them to go f*** themselves. My sister says things like that, but she's a legitimate sociopath who can't relate to other people.
Depression is a trap, but you can climb out of it. Or at least diminish it to the point that it's no longer a major issue. It's not easy, but I'm sure you know that. One thing I suggest is try to stay busy, keep constructive, whether it's through art, studying a topic you like, etc. Sometimes you'll have to push yourself as your condition will make you not want to do things. I don't know how old you are but alcohol and drugs makes it ten times worse, I used to drink to try to forget what I've seen, and I saw a friend of mine destroy themselves in a downward spiral with marijuana where it took over their life. Folks say it's not addictive, and that may be true, but it makes you okay with doing nothing and that'll just lead you to ruin yourself. So instead, focus on making things, doing things, and learning things.
Everyone fucks up. And the fact you try to learn from your mistakes sets you ahead of a lot of folks in the game. It also suggests that you're a good person who wants to do the right thing. I really respect that.
Oh wow I've been there. I'm guessing you went through some hell if you have a general fear of people. I used to avoid people, avoid crowds, and for the longest time I couldn't have someone at my back without feeling extremely uncomfortable. All I can tell you there is take small steps to get more comfortable with people again. For me it was eating out at places, trying to have small talk with coworkers and being nice to folks at restaurants.
You're not insignifigant. Remember that your mood can be very heavily affected by hte things that you tell yourself. Eventually you'll start to notice these 'thought patterns' of things you say to yourself that can drag you down, or up. Some of mine were "the world is a horrible place" and "mankind is rotten beyond salvation". When you get these kinds of thoughts, challenge them. Depression can and does make things look worse than they are. And one of the reasons you may not pick up on social cues is because you're in a lot of pain and you're distracted.
Oh man I feel you there. Families can be the worst. My dad was one of those guys who never took part in raising his kids and spent most of his time locked away in his office. By the time he died I realized I hardly knew him, and as an adult I have very little respect for the man. My mother, while she's got her own issues and she's not all bad, deals with problems by avoiding them... and she saw raising kids as a problem. My brother is a narcissist and my sister's either bipolar or a sociopath. Both my siblings were very abusive and it led me to disown them both.
You can get out of your inferiority complex without being a snob. It just means thinking neither highly nor lowly of yourself. I try to walk that line but I admit I have my moments where I sink one way or the other.
Sadly people will always view thing through their own little lense. The best thing I can suggest for this is to surround yourself with people who can see and apprecaite you for who you are, preferably folks that aren't going to drag you down.
I know how it is to have folks grow distant. Being around a depressive person can be exhausting, especially when you've run out of things to say. Realize that they may be growing distant because they need time to recharge, just like sometimes you too may need time away from someone.
Sadly people always wear their masks, it's part of modern society to put on a false front. Especially in the United States where people are expected to be upbeat and happy all the time... it's very strange and unnatural.
That said, I've been where you're at. Things can get better, it takes work. Personally I've never found clinical stuff to work out for me, but I know it works well for other folks. I ended up having to recover on my own without social help nor medical aid. I guess my first suggestion would be to use google and look up different things you can try out to feel better. I did it myself and it made me get back into my art, music and setting-creation hobbies. I wish you luck, and if you need to chat I'm here. I'm no therapist, but I've been through hell myself and can at least offer a sympathetic ear.

There is a lot to unpack there, but I will say that all sounds very difficult to handle, especially over so much time. Social life and keeping up relationships can be hella tough, but worth it even with some shitty experiences. I'm glad that you are trying, at least. I'm open for some private, more elaborate chatting and hugs if you feel up to it.