rita_gwen,
pro/am doesn't exist all over Europe!
You are registered with only one partner at the same time, anything else is not allowed here.
For social dancing you can do whatever you like of course, but competition couples are fixed, and partners cannot be switched. Many teachers are still participating on comps with their partners, but never with students.
Germany, Italy and the UK are especially great for dancing. If you consider moving to Europe and you have more questions about dancing here, please ask.
komo