Changed over summer?

after a short "thing" over summer which lead to mive heartbreak, i went back to school. When i arrived, things seemed so different. Everyone seems very fake to me and not my real friend except a fair few of course. It's not like im an outcast or anything, i play on the varsity tennis and golf team, dress good , and modestly ok looks;). I feel very cold and distant, they bicker about nonsense. I think a few have noticed,, previously in high school i was known as the funny guy and thats it really, was very skinny. I worked out each day this summer so i got bigger, people noticed and asked me about it, i didnt really respond i just told them yes like it wasnt their business, they try to say something either funny or mature for their "age" and it just seems simple, so i respond simple to them. The people that try to talk to me at school,didnt call me over the summer, is it mild depression. or have i just realized the people i dont care about.