"all of you saying leave, I understand what and why you are saying that but after 6 years and my DD and DSS (who I love like my own, which after that amount of time is the way it should be) it's not so easy just to up and leave, after what is only one mistake with an understandable reason behind it, not a great reason but at least one and not just to fuck you over".
The above from you is the sunken costs fallacy in action and that basically causes otherwise good people like you to keep on making poor relationship decisions. What you forget here is that the damage has already been done.
The idea of sunk cost states that an investment of money, time or energy must not necessarily influence your continued investment of money, time or energy. The past investment is “sunk” into the endeavour and cannot be recouped. It is gone. Ongoing investment will not resuscitate what is gone when the investment is a bad one.
People get bogged down by focusing on their sunk costs.
There are two ways to understand this process, both involving avoidance. One is an avoidance of disappointment or loss when something doesn’t work out. When a relationship doesn’t succeed, especially after a long period, especially after many shared experiences and especially after developing a hope that the relationship would be a good one, it is a loss. It is a loss of what might have been and an acknowledgement that a part of one’s life has been devoted to this endeavour.
Another angle to evaluate is that focus on “sunk cost” creates a distraction from one’s inner truth. The sentence often goes like, “I’ve already invested too much (you write of being together 6 years), so I can’t notice my thoughts and feelings that are telling me to end or change this relationship.”
This is a type of insidious defense against noticing yourself. You enter into a neglectful relationship with yourself which divorces you from your inner thoughts and the quiet feelings that might guide you in your life. In other words, thinking about what already has been may prevent you from deciding what you want your life to be.
The key is to clear away the distractions to rational and emotional clarity. Getting stuck in your “sunk cost” prevents you from this clarity, whether in your relationships or your investments!
re your comment:-
"We are doing loads of renovation work as well which he is doing himself, so he's not all bad and generally quite helpful, kind and sweet".
Your relationship bar is so very low here that it is practically non existent. So because he is doing some renovation work he is not all bad, dearie me. Its a really low bar you've set yourself here isn't it, you may as well have MUG tattooed on your forehead as well as him using you to wipe his feet on. And I daresay too he would not be at all forgiving of you if the shoe was on the other foot.
He does not need to further mess you about, you're doing that now to your own self.