I honestly thought that Aelita would join Team Xen because of the "rehabilitation" she was forced to undergo. I felt sad for her too good work on that one Jan. Yeah I admit that Ren switching sides was a bit sudden but honestly I didn't see it as something impossible. We don't even know him that well and every time we meet, we end up one-upping him so we're hardly friends. The only people he cares about are probably Venam and Melia (probably has a thing for her), and maybe his mom and a few others. The way I see it you're definitely not on that list.
Ren probably has his reasons for joining Team Xen, and they were probably good reasons too.