Of course you should acknowledge this. You need to write him/her then. But you must not ask to many questions, because you can start annoying that affiliate. Instead you should write that you are glad that affiliate is back here, offer him/her help, tell that anything affiliate needs can ask you. If affiliate responds, then later in your conversation (if this conversation is good and polite), you can ask why affiliate left SFI, is everything ok with his family, his life, etc.
