Leave him. It is silly to believe you will be able to change his mind later. You will resent him. What his mum was suggesting is manipulation, which is not fair to him. When men say “I’m not sure” they mean “no” but are not ready to break up. And, honestly, parenting with a partner tests the relationship in ways you won’t ever be able to imagine until it happens. You’ll find someone more compatible if you let go of this one now, but not if you don’t ;)
What a lovely and patient lady. I would probably have answered “thank you” to the first message and not rsvp. There is no way I’d spray my hair to be at someone’s wedding that’s not one of my sisters.