Because you decide to leave home and physically separate from your spouse does not mean you are “legally separated” under Michigan law.
For a couple to be “legally separated” under Michigan law, one spouse must file a request or a complaint about Separate Maintenance. The other spouse must agree to the legal separation proceedings; if the other spouse does not agree and prefers to be divorced, the court undoubtedly will grant the divorce over a legal separation.
All issues considered in a divorce action are considered within legal separation proceedings, including custody, parenting time, child support, property division, and spousal support. The main difference between a divorce and legal separation is that when you are divorced, your marriage is legally over, and perhaps more importantly, you are free to marry someone else. If you are only legally separated, your marriage has not been dissolved, and you are still technically married but only “legally separated.” To marry another person, you must first obtain an absolute divorce. Converting a legal separation to an absolute divorce may mean starting a new action. However, it may be possible to file a simple motion with the court of appropriate jurisdiction asking the court to convert the Judgment of Separate Maintenance to an absolute Judgment of Divorce. Which way you proceed entirely depends upon what your Judgment of Separate Maintenance indicates.
A person might want to have a separate maintenance agreement but remain married for several reasons, such as being able to stay on a spouse's health insurance or religious concerns.