Thanks for your post. Things like this are always difficult! Ok, firstly please don't feel stupid. There are many reasons why this could have happened, the most obvious one being that he had been drinking and was tired. He was probably embarrassed himself which would explain why he didn't say hello to you. This is no-ones fault, it's just the way things happen sometimes.
Just remember to be careful when going back to a guys house. Always tell someone where you are going and only do what you are comfortable with. Remember that drinking can affect you and can impact on your ability to consent to sex.