Just reiterating what others have said.
You said in your first sentence "I have recently started going out with a lovely man, he’s 30." Note recently started going out.
So he's not your partner. He's a fairly new boyfriend.
However dh and I have been together around 35 years, so is very much my life partner, but if I needed to do something on a Saturday night, then he would still go to his friend's party, and go with my blessing. Same as would happen the other way round.
What is odd, to me, is the idea you would both go to a party, then you would leave early and come home and start revising. I mean, that would be odd in my world, where parties tend to finish this side of midnight, but, presuming you are similar age to my dc, they don't even go to the party until quite late in the evening. Surely the logical thing would be to study during the day / early evening, then switch off and go to the party ?
Or
If you are really going to be revising late on a Saturday night, tell him you can't go and for him to go alone.
I just thought that’s what people do in partnerships- leave together because they’re one.
Oh deary, deary me. I have many friends who have been together decades. None of them would ever say anything as vomit inducing as that. Everyone I know is an individual, however long they have been in a relationship.
As some other posts have said, if you became ill during the evening or whatever, that would be different, but that isn't that scenario.