What to do about separate assets that became joint assets?

As a general rule, assets acquired prior to marriage are treated as separate property. That having been said, such property can be "transmutted" (i.e. changed) from a separate into marital property. This can happen in several ways, including the failure to keep the property separate by commingling it with marital assets and or adding a spouse's name to them (it serves as good evidence that the intent was to make the assets marital ones).

At this point you should consider consulting directly with a divorce attorney in your area. They can more fuller discuss your rights in this situation.