Hi again! I still can't seem to find the japanese or english or korean version of this, so that I can actually read it, here is the site http://www.1024manhua.com/jimoshike/.
As far as I have understood, it is about a guy (they are probably college students) who have this sex friend who looks like his ex-boyfriend (or crush perhaps). Although this sex friend likes another girl there seems to be some sort of development of feelings for this sex friend to the MC later on. The crush (or ex-boyfriend) looks like a shitty person.
Google translates the title into "lonely moments" but I can't seem to find it in any other language anywhere.

Hope anyone can help me. Thank you!