I am a little more awake now, so want to try to come at this more fully.
First off, I do assume (hope) you are working with a therapist as long term support for your issues. I strongly suggest that, in addition, you head to the campus mental health center (today if possible, often sign ups for groups things happen in the first week of classes and meetings begin the next week). I suggest you ask about, and try to join:
1. a group therapy/workshop on building social skills
2. a support group for non traditional/older students
3. a support group for those with a history of substance abuse.
Next, I want to reiterate that your reactions are FAR over the top. For you, you returning to the program was the BIGGEST thing going on---it's a huge deal for you. What you do not seem to recognize is that for the others in your cohort it is barely a blip on their radars. They're likely busy figuring out their new schedules, catching up with friends they bonded with last semester, etc. Most who are "ignoring" or "refusing to look at " you are probably just caught up in their own lives and simply not noticing (and it is NOT their job to make a special effort and focus on you instead of their own lives).
Maybe some really are giving you dirty looks and do not like you, but my guess is that you are likely also overreacting to this---many may simply be uncomfortable and not know what to say to you after all that over sharring, so they look/feel awkward. A few may even recognize that you seem to feel put out, want to help and not know how. Others might well be picking up on a vibe from you in which your thoughts about them as mellenials indicates you do not like (or look down on) them and be responding to that criticism by, well, yeah, not liking it very much.
I highly doubt ANY of them have thought "ooooh, let's exclude this person for three and a half years and treat him like a pariah" Quite honestly you are giving far more importance to yourself in their worlds than you have.
As far as being left out of group emails? It's highly unlikely to be malicious. Most people create shortcuts to email a group and just do it on autopilot. The fact that people did not, in the first three days back, of their own accord, think to add you into the precreated list is not some big slight--it's just normal.
Finally, you might never be as close to much of the group as many are with one another, for several reaosns, including:
-you missed out on the bonding early on when you were out sick. This is not your fault, or theirs, it is just reality
-your attitude towards their entire generation, which you made pretty clear in your first post of what the issue is
-being a different generation you might well have differnent musical taste, movie taste, financiancial, work and family obligations, etc which stunt socializing
-alcohol is often present in social situations with grad students and they may hesitate to invite you to things that include it, given all you've shared with them
-they might be uncomfortable around you due to your prior oversharring about your issues
If you were drinking heavily while in classes with them before taking the leave of absence it is also possible that you said or did things that were hurtful to some of them while you were inebriated and some may carry over negative feelings from that as well (and understandably so if such happened)
With the stream of positive, constructive messages in this thread, I knew there would eventually be one person that would not be able to resist the urge to be negative. I am not ignorant. For the sake of the thread I'll hold any further comment toward you. Please don't bother replying any further.
Sigh---this is exactly the type of thing I was posting about in my early post (see below). On a discussion board you do not get to tell people not to comment, nor can you share your issues and ask for advice and then legitimately be angry at someone whose advice or opinion you do not like or you see as "negative"
Quite honestly, assumning that you are ignorant (unaware) of the many serious life issues that many millenials have lived through or are living through and that said ignorance is the reason for your comments is the kindest and most benign intrepretation of what you said.
So it appears your post has been moved to the COmmunity Board. Welcome! All sorts of threads happen here ande very few have anyhting to do with Disney. Lots of people ask for life advice. Fair warning, if you lay out your problem you are likely to get honest advice from many, it seems often posters do not like the advice/commentary/questions they get and seek to control the discussion or limit it to only supporting their view point. It doesn't work that way. If you share---you WILL see posts from all sorts of perspectives, and some might be critical of you or ask questions you don't want to think about.
If you are up for really hearing what people think, by all means post.