Your husband's first cousin never was related to you. You might have called that person "my husband's first cousin." If you continue a relationship with that person after your husband's death, there is nothing preventing you from continuing to use that phrase.
Your father's 1st cousin is your 1st cousin once removed.
second-cousin
your 2nd cousin, or maybe your 2nd cousin once removed.
Your cousin's cousin is no relation to you.
Your mother's first cousin is your first cousin, once removed.
Your mother's first cousin is your first cousin once removed.
If he is your father's first cousin, then she is the wife of your first cousin, once removed. The English language has no specific term for this relationship. If you really need one, you can try "first cousin in law, once removed." But that is too complex for most uses.
Your mother's first cousin is your first cousin, once removed
The child of your first cousin is your first cousin, once removed.
The wife of your first cousin is not related to you.
Your father's first cousin's son is your second cousin. Your father's second cousin's son is your third cousin. If your are asking about your fathers cousins who are in a removed cousin relationship to your father, their relationship to you be more complex, with two different possibilities in each case.
The daughter of your father's first cousin is his first cousin, once removed, and your second cousin.
Your Aunt's first cousin may be your second cousin, onve removed or may be no relation to you at all.