Re: Thinking about leaving
Do you wish to stop with the aikido because you don't enjoy doing it, if so, what is it you find missing in your training now that was there before?
or because you feel you are not advancing enough to help your friends improve their skills and want to stop so they can instead work with someone presumed to be "better" than you feel you are?
if something is missing from practice, then try to figure out what that was, and if there is a way for you to get that aspect back. If it's because you feel you dont measure up to what you feel you should be, then it's definitely something to discuss with your sensei and friends. Likely they'll not feel that you are holding them back and still want to keep training with you.