The questioner asked: "I found a great job opportunity but I'm currently managing a big project. If I leave now I will leave my colleagues in trouble. Should I apply?"
Here's my answer:
One of my sons was in a similar situation a few years ago. His current job was a dead-ender, but he did not want to leave his friends and co-workers in the lurch. To my amazement, he asked me for my opinion on what he should do.
I told him that the best thing he could do for his friends was model the behavior they might lack the courage to do for themselves—namely, leave.
I told him that once he was at this new, better, job, his former co-workers would start calling upon him, looking for jobs. They did exactly that, and he hired a number of them.
As for leaving trouble behind, first of all if you have been a good manager, then they will do just fine in your absence. (If you have not been a good manager, why would you want to stay there, anyway?)
If you have trouble visualizing how those colleagues will miss you, get yourself a bucket of water. Put you hand in the water. Then take out you hand and notice what happens to the hole you left.
for more information, see Do You Want To Be A (Better) Manager?