As someone who was in OP's shoes literally, ( my 1st job was a 4 month contract with an option to extend, which never happened) you tend to shut out people. It just happens. I can't explain it why but it does. I consider myself as a social person who can't live without friends, but i ended up just sitting in my room. When i graduated and while i was working i could never imagine me not going to gym but guess what, i hated going to gym. Heck i stopped going to gym even though i was sitting at home all day. I can't explain why it happens but it does.