Yea man, I have a friend who I got into Parkour, and I talk to him often and yea he's still into training and Parkour, but he sprained his ankle maybe.. 5 months ago and ever since he's been pretty lazy about training. I mean, he does have school and a girlfriend taking up time, but I always try to tell him that he should, and can dedicate a couple hours every week to training :/ I tell him every time I train but he usually doesn't show up.
Been training with him for 4 years or so now, so I'm not really about to say "forget him" Don't let him drive you down, but at the same time you shouldn't really give up on trying to get him to come out. He may come around and in the end it'd be worth it for both of you. Besides, helping others is more satisfying than helping yourself.
Just keep training and progressing. If your friend still really has the "mindset" for Parkour, but is afraid to see his regression causing him to not train at all.. then he probably isn't as into Parkour as he thinks. If he really was, then he'd work to progress back to where he was again and continue moving forward rather than sulking about his down time and doing nothing about it.