SO Slept While Our Baby Cried

I came home from work tonight with my 15 week old baby crying in his crib and my husband sleeping in our bed less than a foot away without any sign of waking! I don't know how long he cried as the last I texted my SO, the baby had been asleep for about a half hr and my SO was going to bed himself. That was an hour before I got home.

Our kid usually sleeps through the night (last two or so weeks) but sometimes this happens that he wakes up for a change or to nurse. Usually I am already home a little earlier and if he does wake up it's closer to 2 or 3 am but not tonight. I just can't believe my SO was sleeping through it! I'm going on a long distance trip in 3 days and now I'm freaked out that he won't wake up to care for our baby while I'm gone for those two nights!

Anyone else have a too-heavy-sleeper SO? How do you deal? It's never been a problem before because I'm a natural night owl. But I will be 1400 miles away!