You mean "left" in the sense that you tell your girlfriend you've "left" your wife, when you still live in the same house, contribute to the household bills, get your food paid out of the same housekeeping money, grudgingly still look after the children on infrequent occasions, share the same bed?
But have spent four years talking about leaving but continuing to have free access to the house and conjugal rights after you eventually move out, and acting offended when your wife tells you that will stop?
And telling your new girlfriend that you can't marry her yet?
And still haven't agreed with your wife on access and maintenance?
I bet your wife and kids will be relieved when you eventually move out of the house.
Does your girlfriend believe you? She must be as thick as Mottie.