“But I have already spent so much time on this. How can I leave it all?”

This statement when thought out loud ignores everything.
It ignores signals, it ignores intuition, it ignores advice and it ignores the truth.

Think about it.
Does it really matter how much time has gone into it, when you know it isn’t working?
Does it really matter how long you have been doing something when you know it needs to change?

No change has ever happened without realizing that change needs to happen.
But once you realize it, would you really want your past to determine your future?