A lot of things could point to either Simon or Riko like (1) not liking Riko praising Simon or (2) not showing the trip diary at home coz he doesn't want Riko to see the hot photo of Simon. On top of that he is super protective of Riko. But there are a few problems with that. (1) the way he safely kept the husk of the cicada that Simon gave him off-handedly, (2) why does he know how Simon's shampoo smells like? (I think he assumes they slept together coz Riko came back smelling like Simon's shampoo), and (3) when he saw the pic in Seiko's wallet, he didn't notice himself who was front and center and instead noticed Simon who was behind him to the side in the pic and assumed Seiko likes Simon (either he has very low self esteem or his eyes go straight to Simon when he sees a pic). I don't know. At this point, my only reason for assuming the one he likes is Riko would be that there is no "Shounen-ai" tag.
I'm confused. Who does Michael actually like? Is it Simon or Riko?