Responses
Yup, it was a flashback. Seme was having a dream about the time when uke just moved in for about 2-3 months.
Here's the panel where he said that:
https://www.mangago.zone/read-manga/kyouju_to_shitsuji_no_shizuka_na_seikatsu/bt/sa-c006/pg-19/
Also uke was feeling sad cuz he was already in love with seme.
So the second couple, seme can just cheat and the uke can forgive him that easily? Yikes not worth reading if it has cheating.