Most states acknowledge de facto
parents -- a person who has a long standing relationship with the child who as taken on the role of a parent. Unfortunately, Michigan isn't one of those states.
The good news is that Michigan is a battleground state for de facto parenting rights, and the laws are being tested. The people at the forefront of the fight are the LGBT community.
Look for an attorney who specializes in family law and who has the endorsement of the LGBT community. Set up a consultation and see if they think you have a chance.
Be aware that along with visitation you'd be on the hook for child support if you're declared a de facto parent.