Honestly, between Mikko and Arvo, I think Arvo's actually the more innocent one. I could be completely wrong here, but I believe the morning hill trek and the scene at the end of day 2 with the black screen were from Mikko's POV, and they make him come across as jaded, to say the least. I'm guessing Mikko had feelings for Arvo (since he talks about old emotions and getting his hopes up again) but didn't think Arvo felt the same way. It'll be interesting to see how he reacts to Arvo's confession.
Anyway, I love Mikko so it's nice to see people talk about him :D I'd love to hear more theories about his route, if you want to share.