It is weird that he said he would pick you over his mom cause "she's already lived for a long time" and definitely not you over his sister. People are really hung up on you asking the question though and your reaction and that's overshadowing what he said. Someone who's emotionally aware would say "of course I choose you" because it was a hypothetical question and it doesnt deserve a serious answer.

I am baffled that more people aren't getting this. These are the kind of fun (well, this one may not be "fun," per se) questions people—especially a couple—ask each other.

My siblings are (other than my wife) my best friends in the world, and we've always been extremely close. But if any one of them had to choose between me and their spouse? Of course I wouldn't win that. I shouldn't.

You've been together four years and you're engaged. Damn right he should be willing to choose you without hesitating and I think you're fully justified in being upset that he'd even have to think about who he'd choose, much less not immediately choose you.

Having said all that, everyone else is also right that it sounds like you should really be in therapy if you're not.