Hi, My name is Philip. I am an attorney with over 16 years experience. Hopefully I can help you with your legal question.
If he is serving a 4 year sentence, then he was convicted at a "General Court-Martial". That is significant, since a general court martial
is the military version of a felony trial.
A general court martial conviction is, in effect, a federal felony conviction.
If the conviction was sexual assault, then most likely he would have to register. It will depend on the state, but nearly all states require registration for a felony sexual assault conviction.
Can he follow you? Probably. There are some restrictions on where a convicted sex offender can live (typically they can not live within a given radius of a school or a park), but any place where there is a military base
there will be locations where he can live.
As for appeals? If he was convicted at a General Court Martial he is entitled, by law, to a full appeal.
The military will appoint him an attorney to assist with the appeal.
The appeals process can take anywhere from several months to several years, depending on many factors. The longer and more complex his trial, the longer the appeal process can take.
It is true, that appeals are seldom successful...that is simply how the process works. The judge at the trial is charged with making sure the trial is fair. But if the judge makes a mistake (and that happens on occasion) the appeal can help the person who was convicted.
You mention you believe he is innocent.
If he is, then I would expect the appeal to grant him some relief
Please let me know if you have more questions...happy to assist if I can