DS is 22 and is completing his master's degree (at a different uni to undergraduate)
He was talking to me how he so much prefers the people he met from undergraduate and his postgraduate degrees to people from school.
DS still talks to his close friends group at school but feels that acquaintances and people he used to talk to semi occasionally completely ignore him now. For example DS wished a few people "happy 22nd birthday" and merry Christmas on social media. He was just "left on read". DS felt a bit hurt to be ignored. DS felt hurt as people would reply with "thank you" and "merry Christmas to you too" in previous years. These weren't complete strangers to DS. They were his classmates and people he'd speak to on occasion at school. He's been wondering if he "did something wrong".
What really hurt DS the most was that a few months into his master's degree a girl he went to school with saw him from a distance and purposely put her head down to avoid eye contact as they walked past. DS was surprised as this same girl had said "hello" to him when she bumped into him on campus a few weeks ago. In the summer prior to starting his master's course DS asked this girl her thoughts on the uni and the girl answered all of DS's questions and said something like "we should meet up!"
DS realises now that she didn't mean it.
DS compares this to his UG friends who still stay in touch with him even if he's not seen them in months. He even finds that people he wasn't that close with at university still talk to him and ask him how he's doing.
YANBU - this was rude
YABU - people lose touch it's a fact of life