I'd dump your girlfriend, stay on your cycle and get a better one when your all buffed and ripped. Ok I'm not serious. I just feel the need to joke.
If you can't fix it your mood swings then you have a choice; deal with the mood swings or stop your cycle. You have to weigh what's more important to you. Are the consequences of your mood swings that bad that they over shadow you progress in the gym? How much do you want to keep your girlfriend?
Sooooo IMO if you can't deal with them and they are making your life unmanageable then perhaps you should stop.
Still if there is a way to use AI's, SERMs, doses, or whatever to control your mood swings so you can stay on then more power to you.