I’m sorry you’re in that situation. By what you explain, I was in a very similar situation 2 years ago. I also quit my 8-year boyfriend because of boredom, lack of attraction. We had become like room mates. Like you, an old flame appeared before leaving my boyfriend, which I think was the trigger but not the main reason. I am not sure if telling your boyfriend is a good idea or whether it’s more something that will make you feel better. Like unloading your conscience. It’s not like you feel sad and I do agree that it might be better to spend some time on your own rather than jumping into a new relationship. Being alone might help you see better what you were actually missing in the relationship and try to get it in a new one.
Also, think strategically. Don’t think it’s a good idea to tell him this bomb while you share the house...