October is about 6 months away and anything can happen during that time. I wouldn't mention it until you have received a formal invitation. Do you want to attend the wedding? If so, when the invitation arrives, do the rsvp and if you don't want to attend, send your regrets. You aren't required to tell them why you aren't attending.
Just my two cents.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.
