30 years ago?
Keith Laumer, Jerry Pournelle, possibly an episode in the BOLOS series?.
As I remember the former mercenary is separated from his unit and can not return as his having sex, married or not, with a person under 18 would earn him the death sentence. The fact that there is no way for him to return makes it easier.
Garde la Foi, mes amis! Nous nous sommes les sauveurs de la République! Maintenant et Toujours!
(Keep the Faith, my friends! We are the saviors of the Republic! Now and Forever!)
LonePalm, le Républicain du verre cassé (The Broken Glass Republican)