So, Yui has to provide for both of them? I don't see this going well in the long run, even if the sex is very, very good.
It's heavily implied in the first two pages that all three of them are working, it's just that Yui is in a place that requires a lot of overtime, particularly on that day. The caption about all three being "working adults", and "You're one [a newbie/entry level employee] too" directed at Yuzu are both pretty clear.