Christina:
I'm sorry - it's a hard decision...
I would show and tell my kids I did the best I could to make it work - counseling, therapy, etc.
I would tell them that it is NOT their fault. They may feel like IF they behave better - things will be better...IF they get straight A's - then it will be alright...IF....they will throw a 1,000 if's at you.
They will get mad...at both of you..my daughter did - she was 9 when we divorced...man - the anger she had was real and huge. She accused us both of not living up to our vows (we have told her from a very young age that your promise is golden and it shouldn't be broken)...yeah - did that come to bite me in the butt...
I would do family therapy as well so that all the issues can be addressed by a NEUTRAL party...so you don't have the slippery slope and uphill battle...
You and your husband MUST keep the kids out of your divorce...it's not their fault.
Don't use your kids against your husband (no, I'm not saying you will but it happens)...
Prepare them for a move - if you can't keep them where they are
Don't say ANYTHING nasty or negative about your soon to be ex...when the kids are around, you two MUST be adults and work TOGETHER for them...
If he gets a new girlfriend or wife - then play nice....
If you have problems with what he is doing - you do NOT tell them what you think...YOU lead by example and keep a log of problems and address them with him when the kids are not around....
There's more...I hope this helps.