One of the differences that really separates successful forex traders from those just starting out is their ability to determine when a losing trade is not going to reverse the trend. Rather than hold and hope, disciplined traders will take the loss and get out much more quickly.
Depends how you define “long”
For me, if it’s broken nearby support/resistance where I was expecting the trade to turn around, it’s time to let go of the trade and cut your losses short.
I don’t have a time frame in which I will exit losing trades
Good point ivanyo, and it’s especially difficult for those traders who flip between different time frames. That’s why it’s probably a good idea to stick to one time frame when you’re starting out, and after you gain experience, you can be a better judge of when to frame your trade ideas against 1, 5, 15, 60, or 240 min charts.
I set my stop loss and it does not get widened, works for me.
A good read on trading losses: The 4 Stages of Loss in Forex | Forex Blog: Pipsychology
I usually look back to my original trading idea. If it’s invalid then it’s time to let go 
If you find yourself in a losing position, then you have 1. not followed your trading plan, or 2. you have not done enough research on the currency pairs, or 3. the market has turned against your position due to economic news.
To fix this just exit the trade immediately and analyse what went wrong and document it in your trading journal.
If your trading plan was at fault revise it and test again and again in a demo trading environment, if your homework/research into the currency pairs was lacking then do more next time!, or if the market has just turned badly then dust yourself off and try again.
You sound like the TheLastBear, unfortunately he has been banned from this forum. Did you open another account here?
Not sure what you are talking about here.
I think it is bad. The more you will stay long in losing position, the more you will make loss. You may loss all of your capital. I think it is good idea to make a calculation how long you will run your trade in losing position and then it is good to close the order after the quote or to use stop loss.
Because emotional it kills you feeling every tick up and down. You will go insane if you don’t learn to cut losses.