I am a lot like that too. Depressed (in a numb way, not a crying way), very socially anxious, can't connect with people, reclusive, etc. Whenever I am with other people I am anxious and also wearing a social mask (which is my alter ego which still has bad social skills) which really wears me out so I just like to be alone all the time. Being around others doesn't seem worth it to me anymore, but it used to.

That doesn't sound immature at all about being hurt about not being invited to the party. That would hurt anyone's feelings whether they would admit it or not. If I worked at the type of place to have a party like that I would surely be the one they would leave out. I've been treated the same way many times, just not in that exact situation.

My mom is also cold and not comfortable talking about emotions. Probably a large part of why we both have these problems today

I don't have any advice but I can relate to a lot of the stuff you said. I'm not very exciting to talk to and have good reason to believe I am weird, awkward and annoying but you can PM me if you ever feel like it