11 Books Found

Based on your description:

"The plot is roughly that the FMC was a princess or noble woman and the MMC was a knight or squire who were friends and fell in love. As they neared adulthood, she was going to be married off to someone who was plotting to harm the kingdom. MMC discovered what the antagonists were planning and was one of the most skilled fighters, so they needed to get him out of the way. Before he could intervene, he was either banished on false charges for a crime or escaped an ambush from the antagonists. FMC grows up thinking he left her or died. I believe there's a time skip at this point. MMC ends up in another country/kingdom. Since he was unmatched in combat skill, he used the alias "Bellum" (or something similar) to make a living as a gladiator/some in-world equivalent. (MMC potentially doesn't return because he believes FMC doesn't want him to, or he thinks she's moved on.) FMC hears about this skilled fighter and gets her hopes up, but doesn't think it's him because he used a different name. "