We can't answer if you should get divorced. We can't answer questions about financial aid.
Your child is now your spouse's stepchild for all legal purposes including taxes, probably financial aid too, although I haven't looked into that in many years.
If you want to keep your finances as completely separate as you suggest, you may need to contact a legal advisor. There are laws covering retirement accounts (IRAs, 401ks and pensions and so on) that may overrule what you think you can do with your assets if you pass away. The spouses may have claims on the others' assets. Your child may have a claim on their step-parent's assets, and you stepchildren may have a legal claim on yours, even if you don't want it that way. These situations are far too complex for this forum.
You need relationship counseling and financial counseling that we can't provide.
