Re: dojo head bans students from training with another teacher (ex student)
My 2 cents. I think it is ridiculous that you wouldbe forced to choose. The way that I have always understood Aikido practice is that it is usually an accepted practice for a student from one dojo to visit other dojos. I have also always believed that seeing how other people teach and learning different ways to do the same techniques is a valuable part of process of lerning Aikido.
Also-I have never been a big fan of the "Sensei is God" attitude that many students tend to adopt..ie, whatever Sensei says we must do, etc. I have trained under many teachers for whom I had the utmost respect and would never do anything to disrespect them in their dojos. However-being told I cannot train somewhere else--that is simply pure nonsense, especially if I am nt given a good reason why.
At one of my former dojos I was training in Muay Thai concurrently with my Aikido practice. I didn't ask Sensei whether or not I could go and do that. It was my choice based upon my own value systems and what was important to me at that time.
I think if you want to support your friend in his or her efforts, then you should do that without fear of repercussion from your dojo or sensei. Heck-worst case scenario-you can always train somewhere else.