"I think my husband would be a bad ex. I think he would deal with divorce by separating himself from the children except for random flashy gestures."
You don't know. You suspect, and may well have good reasons for this. The truth is that if he becomes a bad parent and difficult ex post divorce, well, that's on him.
"I think my children (my son in particular) would be devastated."
You are assuming. You don't know, you haven't asked and your kids cannot form a good understanding of this until you are honest with them about what is happening.
My mum, to this day, still thinks I'm angry at her for divorcing my dad. Couldn't be further from the truth. They were a terrible couple, I could see that clearly even aged 3. She wont accept or listen to my opinion about it though, because she made up her mind about how I feel. That is awful parenting IMO, she is projecting her feelings onto me. Don't make that mistake.
Your kids will most likely be upset by a split. It's inevitable. Some things have to hurt to heal. That's not a bad thing for kids to learn. Not something any mother wants her kids to go through, but with the right approach it can be an ultimately positive experience. Really.
"I think we would be broke and the kids would do without things."
a) He'll have to pay something towards you and the kids.
b) Find out your entitlements re benefits and tax credits. I don't know what your income level is like, but you'll not starve.
c) Money isn't everything. Remember when I told you that the happiest time in my childhood was when my mum was single? She was also a full-time student. We had no money, and I didn't care because everyone was happy and homelife wasn't hard anymore. Quality time as a family is worth more than gold. They'll remember the happy times with you more than they'll remember happy times with a PS3.
"I think I would hate the sharing aspect to divorce. Being without the children for long periods of time."
I imagine that is hard. But not without its benefits. You could spend that time rediscovering yourself, finding someone who'll really love you, retraining, gettting some much needed me-time that us mums go without. The kids would come back and you'd be SO happy to see them, and they you. You'd appreciate the time with them more.
TBH it sounds to me like you've made up your mind to stay. I think that's very sad. You deserve better.
At least try working it out in counselling. Listen to your kids, don't project. Look after yourself, do something to build your self-esteem and perhaps raise your income potential in case he decides to leave you for OW.
Good luck.