At 37, your husband sought out an 18 year old.
At 47, he did it again.
How did relationships prior to you end for your husband? Do you wonder what will happen to James in 10 years and/or is this a pattern slowly becoming apparent to you?
I only mention the above because while what your husband wants to do could be fabulous for partners who want the same, it isn't likely if this is about an age fetish. Love doesn't always mean sexual or romantic exclusivity for everyone. But love never means use up and then treat like a busted toy 10 years later. Only you would know if any of that applies to your situation.
Either way, that he demands this isn't a very loving attitude. He has only know James for two months and this is the first time in 10 years you've seen him behave this way? Is it possible he is having mental issues or something traumatic has triggered this?
If those can be ruled out then it sounds to me like even if you wanted to save your relationship with your husband, he has already told you THAT relationship is over and one you are not sure you want is your only alternative with him
. You might just be selling your self esteem off bit by bit for every little bit longer it buys you with him and still not having the relationship you want.
I too did the whole married in my teens only to be single (with a child!) again at your age so let me assure you - it can be the best thing that ever happened despite how hard or scary it seems right now.
Take care of you and I hope things get better.