Man. This story just feels like too much chapters missing. Someone read the chapter which ...

wasn't it at the end of ch 4.2:
http://www.mangago.me/read-manga/itoshi_no_mirai_kun/nbt/itoshi_no_mirai_kun-chapter-4.2/pg-1/19/
I interpreted it that way at least... he didn't spell it out completly (for us at least) but he did noticed he got ensnared by Mirai-kun and it fits in that he would have confessed then...
... but yeah... it is not totally explicitly said...