1) Harry didn't play the match, sidelines means where substitute and injured players stay.
2) He first felt irritated because he couldn't play the match, but he was quite satisfied when he saw Ginny playing. He was also disappointed because she didnt catch the Snitch.
3) Harry supported Gryffindor's team, they lost the match.

1) Harry first saw his friends and teachers from the Defense Against Dark Art association, and then, while looking for some other members he found himself facing a stone wall. When he turned his face, he saw a black door and walked towards it and finally tried to open it.
2) No, it wasn't the first time, because Harry felt really excited about " finally " knowing what's behind this door.

1) Harry's dream just ended when Ron woke him up with his loud snore.
2) He felt really disapointed because he couldn't know what's behind the black door, but also annoyed when he thought that if Ron had just save his snore for a little more it could have been possible.

Voila :)