well, it seems you are most worried about the emotional impact your trip will have. i can see that you are a first time mom. i have five, so if i sound harsh, i certainly don't mean to be, but i do have a very different perspective.
first, if your son has been night-weaned, then he certainly will survive while you're gone. it may not be easy for any of you, but you all will survive.
and, this thing about feeling betrayed, he's 21 months old (this is where i may sound harsh. i'm sorry.) he will not feel betrayed. he will not ignore his children because of this. he will not hate you when he's 16 because of this trip. he will hate you for very different reasons. lol.
I know, from experience, as a first time mom, you don't want to do anything to hurt him, but if you and his dad really love him and show it well, he will not suffer because of some minor circumstances. think of this as the beginning of life. in life, we don't get everything we want, when we want it, or how we want it. he will survive, and from your concern, it seems he will do more than survive. he'll thrive!
take this time to work and to relax, if you can. i'm sure you don't get much of that. believe me, you will beg for time alone later.
it's great that you're so concerned about your son, but try to put this into perspective. he's so little, has a dad that loves him, a mom that loves him, and so many bigger problems to come. lol. i'm trying to make you laugh. just don't take everything so seriously, k?