I have to disagree with Lokki. Sometimes the choice of quitting is the right one, but obviously it is never easy.
Some people don't start to enjoy flying until they get to fly commercially. Finally free from the constant pressure of the training environment, being pushed by instructors, all while bearing a financial burden. Others enjoy training, and get really disillusioned by the reality of airline flying, and dread waking up in the morning for another boring shift. Honestly, all of us (myself definitely included) jump into this industry with rose tinted glasses and all of us should have put more thought into it!
My advice: It is a great investment of time and money. If you're about to burn yourself out and really are not happy at the moment, you should give yourself a break. Go on a holiday, whatever, just get away from the aviation environment for a while. You have not committed yourself yet to the most expensive part of your training (IR, MCCJOC, TR) so you are not in a bad spot yet. If during your time off you find that you feel refreshed, are no longer stressed, and honestly don't miss the flying all that much, then you know what to do! If you do start missing it, you can always return. You do get rusty, but it never fades completely and comes back surprisingly quickly.
Take some personal time mate, it's not worth being miserable for!