If me and my son's father was never married do I get sole/full custody?

Whatever you think sole/full custody means, the only way you can get it is from a court. Unless and until the father attempts to get some court ordered legal rights, you have complete control and authority of your child and you don't need anything else but the birth certificate showing that you are the mother. As for the income tax exemption, the only way the father could be entitled to the exemption is if the child lives with him for more than the year and he is providing at least of the child's financial support. It does not sound from your facts that he could begin to argue any claim to the exemption.

You need to file for custody. If there's no order as to who can claim the child, claim him but file your taxes asap.

Your son's father has the same right to custody that you do without a court order. You will need to get with an accountant about the taxes because it may depend on how much you make. If your ex- is claiming a dependent to increase his SSI, you may want to file to have that portion of his SSI given to you as child support.

Since there is no formal court ordered custody, both of the parents have rights to the child. In Michigan, a Affidavit of Parentage gives custody to the mom until such time as there is a court order. IRS regluations say that the parent who the child lives with is the parent who can claim the child as a dependent for income tax purposes. If both of you were to claim the child, there would be an audit and the person with the most time with the child would prevail. It may be to your benefit to consult with an attorney and seek a court determination of custody, parenting time and child support. Once there is a court order, both parties would have to comply with it or face possible contempt.