So i guess my question is:

Has anyone been in my place and if so, what happened?

Yep. It takes a rare two people to both enjoy switching roles with each other in a relationship from what Ive seen in real life and online.

Is it normal to not be able to Domme your Master ?

Yes for most people it seems to be and for some reason its easier to submit to one person, but not wish to top them and still be fine with topping others.

Will the mental block go away?

Meh...who knows, maybe if you work on it, though you may also just make yourself and your partner more miserable that way, but at least you will know that switching with the same partner isn't for you then. Not everything in the lifestyle necessarily appeals to everyone else all the time so its not a big deal in so far as acceptance of those distinctions goes so much as a thing to know about one's self.

What would you do?

Try to make it work until I couldn't see it as being beneficial to either of us and then move on. It's a good learning experience and who knows you may be able to make it work out. Your lucky its just an online thing, some people dont figure this stuff out about themselves until they are married for several years etc.

I wish you the best of luck in your endeavors.