Things have been changing recently between Rick and Morty.
Morty used to feel very welcome in the garage. He knew that even if he didn't say it often, Rick cared about him. Now he felt unwelcome, and Morty wondered if Rick still even wanted him around.
Rick had seemed more depressed than usual. Morty tried to talk to him about it, he would get immediately shut down each and every time. "I'm fine," "stop being such a pussy Morty," "don't think about."
He knew that Rick was struggling and just taking it out on him. He knew that him being mistreated wasn't because of something he had done, but that didn't make it any easier.
All the kid needed was a little time in the sun, because god damn he was human and just needed a little reassurance. All he needed was a little praise, some indication that Rick still cared about him.
Morty tried to coax some compliments out of Rick by complementing Rick first, doing anything he asked, and even going above and beyond and doing nice things for him just so he could get a genuine thank you.
Rick had never been warm and fuzzy, but he used to tell Morty he was doing a good job and gave him just enough praise so he would know he's loved without actually ever saying it. That didn't happen anymore.
After a particularly grueling adventure, Morty went straight upstairs and locked himself in his room. He laid on his bed and stared up at the peeling wallpaper on his ceiling. Normally he'd stay in the garage with Rick for a while and see how things went, but he just couldn't take any more insults for the day.
It's not that he didn't have his family. His mom tried her best, his dad was, well, Jerry, and Summer couldn't be bothered to pay attention to anything by her phone and friends from school. He knew his family loved him, but they weren't exactly emotionally available.
He had never felt so alone in his life. So useless, stupid, annoying. He knew everyone around him didn't like him, he could tell.