skyparty L does the unexplained crying shortly into sleep sometimes, and I've noticed it's when he's not sleeping enough, so if he missed a nap that day or stayed up too late he's more prone to having a difficult night. If he's 6 months he might still need 3 naps a day. You could try letting him crash for 20-40 minutes in the late afternoon if he seems to need it, but let it be a stroller nap so it's easier to wake him up, it's a fine balance sometimes, and I pushed L to 3 naps a day around 6 months.
When L has those night terror type sessions we've had the most success with just letting him wake up, take him out of the bedroom, and walk him around until he stops crying, then just let him stay up until he's tired again (usually 1.5 hours later). I find offering him his pacifier or a bottle just makes him more mad. It sucks but L just wouldn't calm himself back down and go to sleep unless we did a reset. Baby Einstein is good then too, so they don't get too stimulated to go back to bed easily, and you can chill as much as possible. If it was really bad we'd give him a bath because that's his favorite thing, he'd relax in the bath, start to yawn and then we'd all go back to bed. Oh and now for the first time at 13 months he can wake up sort of upset like that and cry himself out a bit, interfering seems to make it worse so we just lie with him (after first offering him bottle or pacifier) and he calms down after about 10 minutes. Really amazing to watch because he was not able to ramp himself down at all when he was younger, he's definitely changing these days.
He could also be teething. L would cry in his sleep sometimes, and he woke up screaming too. 6 months is a common time for teething to interrupt sleep.
I'm sorry your husband won't deal with the nights. Would he agree to a split shift? We did that for a while. I would go to bed early with earplugs from 8-1 or 2 a.m., then my bf was off duty until the morning nap. That way we each got 4-5 hours of solid sleep. My bf is a night owl so he would often be up til 1 or 2 anyway, and I adjusted to earlier bedtimes.