blue
What did you learn about relationships when growing up?. Is this the sort of relationship you envisaged?
He is the ways he is for all sorts of reasons and none of them are anything to do with you as a person. You are not his rescuer or saviour here and nor should you be his emotional punchbag any longer. You do not have to waste any more emotional energies on him wondering why he is the ways he is; he is not going to tell you and you are not going to find out. He saw something within you he could and indeed has exploited to his own ends.
Re your comment:-
"it's just difficult to walk away from something I have invested so much in and it has been a gradual process for me".
Read up on the sunken costs fallacy in relationships, that sort of thinking above re investing so much into it is precisely that and that has also caused you to make poor relationship decisions.
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 to much, 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.