Do I need a legal reason to file for divorce?

No. Not anymore; in the old days, of course, you had to have a very good reason (such as adultery or abuse) to file for divorce. Today, courts do not necessarily blame one party for the divorce, which is why there has been a shift to no-fault divorce, which is the only option in many states. The old fault divorce paradigm often resulted in ugly, protracted divorces, replete with high costs, private investigators, and the airing of dirty laundry. No fault divorces are much easier, which is also its undoing in the minds of many, because it makes divorces more common and has often led to lower post-divorce standards of living for women, who often get shafted with less alimony and support than under the fault-only system.