I was looking for a hobby we can continue together for many years until we get really old. [...]
At this point I am so sad that I am even thinking to stop dancing altogether. I lost my motivation....
This is sounding a bit different from before.
I know much of what my husband likes about dancing is the thought of dancing with me... for many years until we get really old. So the question I have for you (and which you might want to explore with yourself) is whether your
real inner fear is that this dancing dream goes away if she moves into competitive dancing, becomes used to much flashier dancing than you are able to do and so you are no longer dancing together? And if so, they your hope of dancing together when you are old would seem to be vanishing?
That's somewhat different from the physical jealousy issue (and of course, these things aren't always either/or.)
Anyway, if your fodest hope is to dance together, I would actually suggest going out of your way to find and attend social dance events. I don't know what's available near you. But around my home, it's possible to find bars that have bands that pay swing/salsa/hustle and various club dances. There are also studios that have friday or saturday night practices. I would suggest finding these and trying to schedule a "dance date" at least
once a week with your wife. You could, in addition, organize any lessons you take around improving your ability to dance the social dances that fit your dance dates. ( For example: there is no way I could find argentine tango dance events in bars around here. But East or West coast swing, night club 2, cha cha, salsa and most club dances are easy to find.)
It wouldn't hurt to organize going with some other couples either.
This might not solve your jealous feelings when she dances with her pro. But if you are going out regularly, and dancing, it might make her fell more interested in learning dances that
you both dance socially. It's New Year's. I'd honestly suggest making it your resolution to try to go on
at least 2 dance dates a month in January and February. (Eventually, you want to go more. But you need to find places first!
(If you don't know how to find these things: learning names of local bands and following them on facebook helps. If you go to a bar that lists upcoming bands, note all those bands down, hunt them down on facebook, and you'll learn which places schedule bands.)