Husband fell asleep and didnt hear toddler wake ...?

Im with our newborn girl, and i wake up to our 18 month son screaming in the next room hitting the wall / door. I lay there for a minute thinking surely my husband is there but the fact I can hear my son hitting the wall / door maybe not. I go and open the door and the poor baby is just alone and screaming. I give him the biggest hug and put him back to sleep

I go downstairs and my husband has the tv on loud, asleep. Baby monitor is there, but he must've either not heard it over the tv or he was in way too much of a deep sleep because of the 'devil's lettuce'. I dont have an issue with that usually...

Im heartbroken for my son, ive co slept with him since lile 6 months, to think he was alone and scared really upsets me. It must've been long enough for him to get up and start thrashing around. Then its like why the hell did my husband not wake up, how could he sleep through the screaming. Its so dangerous what if my son hurt himself

I dont know what to do? Maybe im just venting. Im upset