this isn't really a note on the translation because the focus is on what isn't said, and i probably should add a disclaimer that this is just my take
that's a more delicate/family-friendly** way to put it
你都不知道晚上我怎麼想你
"you don't even know how i think of you at night"
how, not how much. how, as in "what positions i'm putting you in while i'm jerking off" how*
this is one of those instances where the actual translation doesn't matter as much as the implicit meaning. by now we've been given enough clues and context to key in on what Yuan really meant. Yuan has learned from his drunken confession that going too hard (ha) would cause Qian to shut down. he's learned the art of subtlety and how to keep the heat simmering (that whole "coming in directly" double entendre and that offhand bondage comment plus how many times have we seen him feed Qian creamy white substances (i.e. milk and porridge) please the dirty jokes are right there). i do think the expectation is for the audience to easily fill in the blanks (ha), because it should be really clear what Yuan's implying: he's been masturbating while thinking of Qian
*that was my first thought as soon as i heard what Yuan said anyway. decades of media consumption and picking up words and euphemisms and hidden meanings conditioned my brain to automatically make these kinds of connections
**side note: i've never watched anything else on youku and i don't know if their translations need to be clear of any swear words and suggestive language, but there were multiple instances of swearing that didn't get translated (Qian x5, Yuan x1, Ah Hu x1, Le Ge x5 just off the top of my head) plus that cleaned up "coming in" innuendo. i've pointed out the ones that make the most impact in earlier posts