I have been married to a man 50 yo and I am 46. Rather childishly but I keep feeling jealous of his ex wife and that he doesn't love her but cares for her well being because he has 2 kids with her. He loves me immensely and says so as well and I don't doubt it.
But it is weird that he should even consider that I should be friends with his ex.
It bothers me more because at this age I can't even have more kids. I always feel like that he shares more with her than with me.
Why do I feel like this? Is it wrong? What should I do?

This strikes me as odd - "I have been married to a man..." It sounded so distant for someone in a relationship and married to this person. As an example I wouldn't say "so I am living with this guy" but rather "I live with my boyfriend."

But anyway you need to come to terms because that "man" and his ex share kids, there is always going to be a relationship with the ex. Would you like him more if he totally ignore his children? I think not. So get past it and don't had pressure and stress to your relationship by something you can't control and need to accept.

That is just my two cents.

How does your inability to have "more" kids factor into this?

I give your husband credit for keeping a friendly relationship with his ex-wife, very possibly for the sake of their children.

I'm sure his children can spot your attitude and feelings toward their mother. That doesn't feel good to children.

Tell him you don't want to be her friend - I suspect that, if you can't tell him this and he doesn't realize it, the problems are far deeper than your jealousy of his ex-wife. If he confides in her instead of you, I'd ask him why.

Jealousy comes from someplace - past betrayals, fears, something else. What is the history here?