Morning
"Me and my bud are both married but we get together once in a while in a hotel suite and spend the day chilling and bating. He stays hard for a long time after he shoots his load but mine goes soft right away. Why?"
Immediately, completely soft? Or, does it go down gradually?
Are your bate sessions later in the day or evening? If so, it could be testosterone levels, which become depleted over waking hours. But it isn't something to be overly concerned about.
Is there an age gap? The older we are, the faster the boner wilts and the longer it takes to recover for a second or third round.
Do you feel a sense of guilt over masturbating with a friend, perhaps like you're both cheating on your wives? Guilt can be a powerful thing - though jacking off shouldn't be considered "cheating;" even if it is with a buddy, it's still solo activity.
That said, the amount of time it takes to lose an erection after ejaculation will vary. And it will be different from guy to guy. Does he continue to stroke his cock and play with his balls after he cums? That could be what helps to keep him hard.
Continued stimulation after you cum should at least slow the process.