Jemima,
re your comment:-
"We have been together 5 years so it's difficult to walk away"
This is really called the "sunken costs fallacy" and that basically causes people to keep on making poor relationship decisions.
People get bogged down by focusing on their sunk costs. You are bogged down. What you're also forgetting here is that the damage is already done.
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.
What does this latest episode tell you about him?. He cares more about his own self than you.