I'm sorry you're going through this. Can you ask him if he would be willing to try couples counseling 1st. If the answer is no, then I suggest accepting his offer to separate. A relationship needs both people who are willing to work to improve the relationship. If his mind is made up, then no use delaying the inevitable. If he does want to stay he'll likely end up doing this again which is why counseling is necessary. Your kids will survive a break up as long as you both remain civil and respectful for your kids sake. I wish you well in getting treatment to feel better.