Why didn't he ever tell her that he was involved with/lived with someone?
How old are the two of you?
Did she speak to him?
Thank you for that additional info. The thing that I would be most concerned with is that he did not tell her he was in a relationship and he's been in a relationship for a year. That tells me that he wasn't ready to let go, or he cared too much to hurt her feelings. I don't know why she broke up with him, but it would be reasonable to assume that he may not have gotten past that blow, and is wanting her to show that she wants him, or is still interested in him, to soothe the fact that she chose to break up with him. This doesn't necessarily mean that he wants to be with her, just that he's still hurt and a part of him needs his ego healed.
So my question would be, does she now know that the two of you are together? His answer to why he hadn't told her was a non answer, and he needs to address that. If this is the only issues you've had so far, I don't know that I would say that you should be worried or concerned all the time, but I would want to know that she is crystal clear that the two of you are living together and have been together for a year.
I welcome your thoughts, let me know if you want to talk more
Isn't it interesting how he can keep in contact with his ex every week, and when you find out about it, thats when things start 'getting old'? I know you care about him, but you have to look at the big picture and ask yourself if he ever got over this woman. Not something you want to think about, i know, but you have to. You have every right to know why he was in contact with her all of this time, and why he chose not to tell her he was in a relationship. The problem is, HE may not want to face up to the reasons, and thats why he's angry at you for trying to make him face it.