Hi there PTM!
Sounds to me like he's got a bit of Separation Anxiety from your trip without him.
We don't typically reccomend cry-it-out based solutions here on the site, as that's not a technique that Tracy would have reccommended, for a number of reasons.
If you have left him to cry, it's possible that it may contribute further to his separation anxiety worse. What I'd suggest is having a look at the links that I'll post for you that discuss two techniques: gentle removal (of yourself) and walk in/walk out. You can decide which will work best for your child. Typically gentle removal works pretty well with toddlers who have separation anxiety.
In your case, since it's just at bedtime, not all night long, you might want to try sitting in a chair near the bed, and then moving farther away each night until you're out the door. And then after that, try Wi/Wo if you're still having troubles.
Hope this helps!