@Balthazar007 The first scenario I thought of was for them to be close childhood friends (maybe Bolis being an older brother figure). Maybe the dads were close friends before that and that encouraged their friendship. Or if he's a bit older than I'm thinking, Bolis could have been introduced by his Dad for tactical/political gains. 7 to 8 years sounds like a good number for this scenarios.
How about, since my character is 8 years older than your's, we go with they are good acquaintance. Both from Sutisu capitol, they may not have been formally introduced, but they met at one of the many galas/balls. Bolis or Sun was hiding away from the party, and the other one also stumbled upon the same hiding spot. This desire to escape the crowd is what they bonded over. They continued to have these encounters over the years, forming a quiet bond and a mutual respect. They didn't hang out together as friends outside these gatherings.
That first meeting was when Bolis was 15 and Sun was 7. Bolis stayed in Sutisu city till he was 23, studying logistics, like his family usually does. When he reached a certain level, he left to go join the military. So this would put Sun at 15, and they would have been "friends" for eight years.
They wouldn't speak to each other again until a few months after Sun gained control of the crystal. By this time, Bolis was already a high ranking officer, but not a General. Bolis offered his condolences, but they didn't start hanging out or anything. They both had too much going on in their lives. They did, however, start calling each other on occasion, to stay in touch.
Since Bolis became a general (2 years ago), Sun has started visiting him in person once every few months or so, at Bolis's request. While other Generals see Sun as a mear tool that isn't doing enough for his nation, Bolis sees a young man, a friend, who has had a great burden thrust upon him. He sees Sun's potential to help the war, but he also doesn't want to push the young man into doing anything he doesn't want to do.
How does a that sound? Anything to add/change?