Tisha B'Av is now over but the message we can take from this day should stay with us. One of the main purposes of a fast day is to get us to do teshuva. If we stay where we are and don't decide to change, then what was the point? We need to show Hashem that it bothers us that we are still in galus and that we really want to come out! We need to make real changes so that Hashem will see that we care and we don't want to be in this dark and bitter galus anymore.
We know that the Bais Hamikdosh was destroyed because of sinas chinam which means baseless hatred, having bad feelings towards someone with no good reason at all. So to correct this, we need to have ahavas chinam, love other Jews for no good reason other than because they are Jews! We need to work on ourselves so that our hearts are overflowing with love for one another so that we wont ever want to hurt someone intentionally and we should keep on looking for ways to be kind to others and make them happy.
The famous story of Kamtza and Bar Kamtza talks about how a man was making a party and somehow the invitation got sent to the enemy (Bar Kamtza) instead of to the friend (Kamtza). When Bar Kamtza showed up at the party, he was embarrassed publicly by the host of the party and was forced to leave. He was so angry about this that he reported to the Government and this was the first thing that actually brought about the churban, the destruction of the Bais Hamikdosh.
The question is, why is this story called on Kamtza's name if he wasn't even at the party? He had nothing to do with it! In fact, he may not have even known that there was a party that night!
The Maharal says (I heard this at a speech by R' Viener) that having a good friend is only good if it is not to the exclusion of anyone else. We all know about how much we want to feel part of things and included in the group and how it hurts to be excluded. Cliques are very dangerous. We have to make sure to include other people in our friendships and go out of our way to make others feel like they are part of it too. So yes, Kamtza was responsible too since he and his friend, the host of the party, did not include Bar Kamtza in their friendship.
This is the message we need to take from Tisha B'Av. We fasted, we cried, we davened and we hoped. And moshiach still isn't here. We need to work on being more pleasant and friendly to others. We need to include others, be more aware of other peoples feelings, say a kind word, try to compliment more often instead of criticize, speak positively about others instead of put them down and think of ways to make others feel loved and appreciated so that we can show Hashem that we are changing for the better and that we really want moshiach!