I was writing the conclusion to one of my short stories in which the main character has to endure a bit of humiliation so that everyone else gets to have a good time. The closing sentence is: They keep the high, but he took the volume. To clarify, it's a reference to the lingo used by meth junkies, where "high" refers to the heightened feeling as a result of the drug's immediate interaction with the nervous system, whereas "volume" refers to the unavoidable noisy after effects of the substances. Coming to the tense, I use present for everybody else because I mean to convey that they still cherish that memory, but simple past for the main character because he took the bullet and then got over it. However it still doesn't feel grammatically accurate. So the point is, 1) is it grammatically correct? and 2) if not, what's a better way to put it. Also do not dare to use that line in your own work.
Both the simple present and the present continuous sound a bit off combined with simple past in that way. Also, keep may not be the best verb to use, holding, clinging to, grabbing, riding, surfing etc. may be better.
Difficult to say what would sound better without knowing the preceding paragraph, but maybe use past continuous: "They were holding the high, but he took the volume." Or my pick: "They were riding the high, but he was saddled with the volume."
Edit: alternatively try using the word "still" in the first half, along with present continuous - i.e. "They are still keeping the high, but he took the volume" or use because in the second half with the past tense - i.e. "They keep the high because he took the volume" either works