I’m very much confused here right now

RUN. She will control your life!

Nuh uh. You need to have a little chat with your partner, let him know that is not okay. She will steamroll you, him, and your life otherwise and have everything revolve around her, her preferences and her feelings no matter what's best for you.

Run. Run far. Run fast and do not look back.

Honey, I want you to consider very carefully if you want to be second fiddle to his mom for the entire rest of your life because unless you leave now, that is exactly what is going to happen. He BOUGHT HER A RING, he’s not going to change now.

As much of a cliche "DUMP HIM!" is on the internet. Like... There's a lot going on here and none of it good. The enmeshment, obviously. The fact that she feels entitled to be up there and that he saw absolutely nothing wrong with that notion, apparently. All galling, completely. But the fact that he didn't think to tell you, or actively hid it from you is possibly the bigger flag. This is a glimpse into your future, and at the very least, until you're all on the same page (ie: in the realm of sanity) on the fact that his mother is trying force her way into your wedding, you should be postponing the wedding to try to see if the relationship is worth saving.

Oh hell no. Engagement over as far as I’m concerned.

Please don't go through with it. Run from the narcissistic mother and her manchild.

With any luck, you'll have a son that you can marry. This is the re-boot of Oedipus Rex where he doesn't tear out his eyes!

This marriage is going to be hell unless proper boundaries are set