I will tell you the story of both when I felt my most helpless/childish as an adult, AND the loneliest thing I've done.
I was in college. I thought I was coming up from the "bottom" of my depression because I felt like I was on track with my medication after my suicide attempt and subsequent stint in the psych ward, but it turns out, I hadn't seen the bottom yet.
I was not healthy; my three roommates whom I considered my 3 best friends/sisters could not deal with it. The girl I was closest said she "couldn't do this" and left, but the other 2 girls sat me down one night after I had gotten into bed and told me they were renewing the lease for the apartment for the next year, but they didn't want me on the lease. I didn't understand at first, and then I understood and started crying. One of them just left the room quietly; the girl I shared a room with started rolling her eyes and sighing, and then got up and got ready for bed.
I left the apartment. I drove to my mom's house, which was only a 10 minute drive, but I had to keep pulling over because I was crying to hard to breathe, let alone see and drive safely. With the encouragement of my now soon to be ex-roommates I'd bought a Carebears night shirt for nostalgia's sake a few months prior; I was wearing a carebears nighty and some pajama pants, and as I had been ready for bed I wasn't even wearing a bra....I got out of my car, wearing a fucking childish nighty and pajama pants, and knocked on the door of my mom's house at like 1am. She came downstairs and saw me, clearly new I'd been crying and just said, "Oh my god, what happened?!" I fucking lost it. I have never cried so hard in my life. That was when I felt my most childish as an adult; standing on the doorstep of my mom's house, just fucking losing it and sobbing, in a goddamn carebears night shirt, while she was hugging me and trying to understand what happened.
I crawled onto her couch after telling her what happened; I passed out. I did not go to class the next day, or the next, or the next... I had an emergency appointment with my therapist. I didn't understand anything. I had a lot of unanswered questions, and she told me to send a message to my roommates and ask for specific reasons why I was being (essentially) kicked out.
They all responded very...truthfully. But the messages I got back were essentially the long list of reasons I hated myself; that circle of self loathing that keeps you trapped in depression-all of my own secret fears and worries laid bare. 3 separate people, the 3 people I loved the most outside of my family and boyfriend, laid bare all of my faults and insecurities.
Nothing my family or boyfriend said made me feel better. I felt like my therapist had steered me wrong (in retrospect it was the right thing, to find out why). I wanted to die. No, I wanted to actively kill myself and leave my body in that fucking apartment after smearing something like "YOU DID THIS TO ME" in my own blood on the wall. BUT my medication was working, and I knew that was fucking stupid.
Something like 5 days after I'd gotten asked not to renew my lease, and 3 days after getting the facebook messages, I told my mom I was going to class. (I hadn't showered in those 5 days). I drove to the grocery store in my fucking pajamas and bought a gallon of rainbow sherbert. I waited around until my family was all gone to work/school. I went back to my mom's empty house, and laid on the couch and ate the sherbert directly from the carton and watched Disney's Fantasia on VHS, until my mom was due to come home. Then I drove to this place that overlooks the city I live in, and parked my car there. I used to go there when I was feeling depressed, usually with the girl I felt closest too, and sit at night and look at the lights of the city. I just sat by myself until "class" would have been over, and then I went back to my mom's house and pretended like I'd been to class even though she knew I hadn't. That was the loneliest thing I've ever done. That whole day.
I had plenty of people who would have been there for me. But I felt so misunderstood, that's what I decided to do instead.
I'm in a much better place now. But I still have a lot of anger and resentment in me from that period of my life. I rarely go to that part of the city anymore.