Emotionally, I agree that whoever ends the engagement, the other person should get to keep the ring. However, I think the law, in most states, is that an engagement ring is given in anticipation of marriage (which is a contract.) If the marriage doesn't take place, the contract is not fulfilled and the ring returns to the person who purchased it. I don't have a degree in law, but I do watch the Peoples Court when I walk on my treadmill and I did stay at a Holiday Inn Express a couple of times!!
A bigger question is, why did Mike, after waiting almost 90 days and still not being sure if he