It's in the wording.

My issue with this is not Aki admitting he still loves his wife since It makes perfect sense. She died it's not like they got divorced or ended in bad terms. He is more than in his right to still have feelings. My issue was how he decided to express it. "I'll be unfaithful to you but I will still take you up on your feelings and touch you" add to this the fact that he never actually told Kei that he loved him or any sort of solid confession aside from I wanting to fuck. Does he like him? he certainly does have feelings for him but they feel more like an enfatuation.