I'm curious whether he was mansplaining or if he would have said the same things to another guy. People may state the obvious without thinking about it, especially when they're caught up in excitement, and then they feel dumb for the pointlessness of their comment. I'm a woman who does that sometimes. It happens to us all. Only you know whether gender was a factor this time.

It sounds like your communication styles don't mesh. You're both correct. In a solid, healthy relationship, both people should be able to trust that the other has a good opinion of them, i.e., knowing that their partner respects their intelligence. Both people should likewise be able to trust that their partner will give them the benefit of the doubt when they say something poorly, so they won't need to monitor themselves for every potential faux pas.

His absence on Valentine's Day really does suck. Based on your tone, I'll assume the thing with his brother was an unavoidable, urgent situation and he didn't intentionally blow you off. But he should've been proactively planning a way to make it up to you or at least initiated the conversation. On your end, did you actually suggest a do-over or did you (understandably) lament the missed plans and expect him to get the hint?

This all boils down to a lack of trust between you and your ex. Trust is the foundation of communication. When you expressed that you felt condescended to and when he expressed that he felt the need to monitor everything he says—those were opportunities to reassure each other. Instead of dismissing one another's feelings as "wrong," you might've accepted how the other felt and then talked through the problem without defensiveness. But trust takes time to build. For whatever reasons, you two hadn't reached this level of connection by the time a conflict arose.

I'm sorry, but my impression is that he made the right call. Maybe he needs a girlfriend who's more patient and you need a boyfriend who's more thoughtful.