He won't forget you. I think the longest I ever went was three weeks - which is nothing like as bad as some of you - but that wasn't like a normal three week absence during the holidays for example, it was three weeks of everyone knowing he was permanently witheld. And it happened quite a few times which was awful for my son, so when he saw me again although he was really happy to, he also became a bit guarded at wondering if it would happen again. At that age they haven't quite learned that degree of self protection to be too guarded, they are just confused but bounce right back once they start seeing you again. The reason I know they don't forget, is my son didn't see my partner for a year and he was only 6 months old when he first met her. When we were "allowed" to all be together, he knew her instantly and had an instant bond. Even the solicitor said - he already knows your partner if he met her when he was 6 months old.
It's not just about "memory" - it's bigger than that - it's about "knowing" someone - smells, sounds, past feelings of security with that person etc. I guess it's about love really. Which is why you can't quite describe it. People talk about a bond and there is that as well, but when there is love you always know the person.
He won't forget you. He may have his own little world where he tries not to think about something he can't have and secretly wishes for it now and then.
You'll get there.
Daddy - I 100% agree with that - slow progression is rubbish - what they need is stability and a normal life as soon as possible and a routine that makes them feel secure again. A slow progression and long absences can actually just increase the anxiety that you might disappear again.
If and when you do get to see your son again, don't forget, at some point (not straight away) to tell him that his Dad is always there and always wants him. So he has that knowledge.