What's is the difference between the following sentences:
1.if I wanted to leave, I would leave now.
2.If I had wanted to leave, I would have left by now.
The meanings are basically the same in your two examples.
The slight nuance might be
1.if I wanted to leave, I would leave now.
means you are talking about considering leaving right now, whereas
2.If I had wanted to leave, I would have left by now.
means you were considering a some point before.