We don't actually know that he's been deceitful, leading OP on or lying etc. He may have been open to the idea of more kids previously but as time has gone on and he is feeling closer to 50 he's realised that bit of his life is over.
The point is, whatever his reasons, original intentions etc, where he is Right Now is on a different page to you @Needinglifeadvice .
Previous posters have said it all really in terms of regrets/decisions for you. Some good things to think about.
I don't want to bash the age-gap relationship as we also don't know much about that and you've clearly been together around a decade but I would say, in terms of weighing up future life options, it is worth considering that the likelihood is that you will have a significant chunk of your later life without him. At that point, it could be quite lonely and you will be past the stage of having the option to have children by then. When you picture yourself in your 60s, or in retirement, what kind of life do you want? Who are the people around you? What is your time filled with?
Of course, it is a gamble and there are no guarantees that you will have children even if you do leave him. Do you think you would feel better for giving yourself that chance? Or can you make peace with a comfortable life with this man you adore? Can that be enough for you?
Personally I would have had to end my relationship if children were taken off the table. When I met my Hubby we did talk about family stuff early on, as he had a daughter already and it was important to me to know if he wanted more children. I can only imagine how mixed and difficult the feelings would have been if he'd said no, as it's hard to meet someone you click with. Thankfully we were on the same page but I still know that, I would have personally needed to explore that opportunity via every avenue possible before giving up on the idea of kids. For you, that decision may be different but only you can know how important it is to you.
Lots of luck.