How can I find out if i qualify for an exception on Married filing separately I had 3 dependents that are not his he has 0

What exception are you referring to?

By "exception", do you mean, do you qualify to file as Head of Household instead of Married Filing Separately?

Even if you were legally married as of December 31, you're considered unmarried (and therefore eligible for Head of Household) if all five of these conditions apply:

1. You won't be filing jointly with your spouse
2. Your spouse didn't live in your home after June (temporary absences due to illness, school, vacation, business, or military service don't count)
3. Your home was your child's, stepchild's, or foster child's main home for more than half the year (non-child dependents in your home don't qualify)
4. You paid more than half the costs of keeping up your home during the tax year
5. You meet the qualifications to claim the child as your dependent, even if the other (noncustodial) parent is actually claiming the child as a dependent on their return

You can also be considered unmarried for Head of Household if your spouse was a nonresident alien at any time during the tax year and you're not treating them as a resident alien.

I'm so sorry for you loss.