The last person Steve needed getting flayed was you, his girlfriend.
Possession wasn't easy on anyone, but the way your broken mind begged and pleaded, snapping at anyone who came close, simultaneously tugged at Steve's heartstrings and made him feel downright sick.
Thankfully, whilst the Mind Flayer was strong, your body simply did not have enough muscle to accommodate its strength. After meticulous planning, the group had managed to knock you out, using the limited time to tie you up and literally weld the steel handcuffs onto a pipe, and chained legs to the floor.
It was cruel, sure, but necessary. The room you'd been locked in was dingy and small, the heating cranked up, attempting to buy enough time to destroy the source.
Meanwhile, Steve found himself lingering around, putting together sandwiches and trying to get you to eat them, or maybe even drink some water.
Your body was still human, after all. But the Mind Flayer didn't feed off regular sustenance, so each time you refused, hissing and yelling and pleading to be freed. This was another of those times, and despite knowing the outcome, Steve still found himself leaning over your restrained form, muttering hushed words as the sweltering heat inflicted a physical pain upon its host.
With the temperature rising slowly, it was only a matter of time before the Mind Flayer would be weakened enough for a momentary retreat, where Steve would be gifted mere minutes of clarity with his girlfriend.