A.J.
I don't know what to say about the bed wetting which will of course pass. But you need to SERIOUSLY shift focus in your home.
I'm divorced after a long separation and my kids' dad ALWAYS traveled 95% of the time. In other words: There dad has NEVER been there for more than a couple days here and there since they were born. Sometimes a week or two here and there. I know many families in the same boat as their husbands have the same profession. There are two ways of handling it 1) the happy way and 2) the extremely miserable way that harms the kids.
The happy way is to ACCEPT WITH GRACE that the dad is NOT in the picture. He is NOT to be depended on for important things. He will NOT tell the truth, he will NOT hold up his end of bargains often financially or otherwise, and therefore he is NOT the focus of your family. You do not TEACH the kids that they should depend on their dad and be heartbroken when he doesn't do x, y, z. The tiny child doesn't even have any idea they are being let down, unless someone tells them.
In our home, I was (am) the happy leader. We have a happy family. Sometimes, SURPRISE, their dad comes to visit. I never let them know in advance because it most likely will be canceled. Every time he comes it's a big fat fun celebration for them, and then like always, he leaves. Then it's my job to carry on as if everything is fine. Which it is. I sympathize with the tears for an hour or so, and then we're on with our busy schedule. The kids never hear me say their dad is a cheating, lying, irresponsible, selfish person who is three months behind on child support. That's none of their concern as innocent little kids. All they know is their dad loves them and sees them when he can. As they grow older, hopefully I'll meet a proper man to set the right manly examples in life. Meanwhile, we're happy. I caught my ex making empty promises once to my son about something they were going to do together and I BIT HIS HEAD OFF (when kids were not in ear shot) and told him not to EVER EVER EVER blow smoke up their asses or I won't be the nice, agreeable person he knows. He still accidentally does it at times because he's a bullshitter who lies to everyone, but I chime right in cheerfully, with "Actually we don't know what papa's work schedule will be in 6 months, but we'll see how it goes" and I shoot daggers at him.
This has worked well for us. Mine are 9, 7 and 5 and have NEVER asked if I would leave them just because their dad flits in and out of our house like a moth. I'm their full time mom. It's what they know. That's OK and normal that your son asked that, and good that you answered, but don't let your house have uncertain and scary vibes by acting confused yourself.
On the other hand I have friends who have tried to make their husband/ ex husband tow the line and let the kids try to depend on him like a normal dad and then suffer all the disappointments and hear the mom's frustrations. That does NOT WORK WELL. The kids are miserable that way, parroting the mom's disappointment over every little lost thing the dad was supposed to do. Lamenting how much their dad lets them down. Learning from others (well meaning friends and family etc who sit around griping with the mom about the absentee parent) that they're supposed to be upset by it.
You can't afford to and will not fly kids to him. Period. He isn't coming to see you guys. Period. End of worrying about the visits that aren't going to happen. If he starts showing up sometimes. Fine. He can let you know when he makes that happen.
You will not change the situation. You have to change the perception. Don't let your husband try to get sympathy with lame promises about cliche dad things to your kids. Don't let your kid pine away and be hopeful about dad and then disappointed. Take charge and direct your family in a positive way. Your ex will keep up with you guys or not.
My ex has REALLY stepped up in lots of ways as we move on happily through the years. The kids are high achievers and he comes to their events when he's able and likes to take credit for all the stuff they're doing..he'd probably be scared to come see them if I was the disappointed, guilt-tripping ex I could choose to be. Not saying you will do that. You owe it to your kids to focus on them and yourself and the real world on your plate.