Well it was a remark regarding the fact that people being lazy (having student-style drunk nights) seem to be paid disproportionately high salaries
Who 'seems to be paid disproportionately high salaries'? Nobody has told you how much they earn. You've just made up the salary thing in your head.
I thought in the adult world, there was no time for that
Why? Why would there not be time? Regardless of salary, adults have some leisure time. I don't know anyone, on any salary, who works from morning until bedtime, seven days a week. Spending an evening having a meal followed by a few drinks in a bar doesn't take up any more time than, eg, watching television all evening or going to the cinema.
So how did your work colleague end up having sex with you without overstepping multiple red lines? That's the part that's not making sense.
There was an obvious mutual attraction between us, lots of flirty eye contact and body language which we both responded to. It would have been very clear to me if he hadn't been interested in me, and vice versa. No line was overstepped because we were both sending obvious signals to one another that we were attracted to each other. It wasn't a case of him 'making a move' on me; it was a mutual thing.
If reading those signals is something you find difficult, then of course, online dating is probably a better option for you. We're all different.