It's been three years, if not more. Was she that much of a big deal that he still wants to die?
The girl was not only his Childhood friend, and practically the only friend his age from the Orphanage. (Everyone from their Orphanage has the family name Bruce) So his dream job that he worked super hard for was crushed, and then that same day he was rejected the girl who planned to have a relationship with him announced she decided the day prior to become one of Jian's mistresses. So yeah, the girl was a huge part of it, but basically every dream the guy had died that day.
At normal engagement ranges a ballistic weapon would be perfectly fine in the vacuum of space in terms of it's firing profile. It's only at really high max ranges like sniper and beyond where the laser's ability to instantly traverse the space and be less influenced by any nearby gravitational forces comes into play. If anything ballistic ammo is better in space than it is on land, as the lack of drag and less wind means it will lose less energy or go off target less in that environment.
Plus, if everything is built to combat the high heat of lasers via reflective or dampening armor, then ballistic weapons would punch right through those defenses with ease.
The major downside to using ballistic weapons in the vacuum of space is that you would need some sort of opposing explosive force that triggers with the same impact in the opposite direction, or an anchoring mechanism while firing which would make you immobile, or the impact of firing would blast you backwards and throw you into whatever is behind you.
Generally speaking you would want to use both in tandem, to avoid a scenario where your enemy is able to completely negate your arsenal with the right type of defensive measures.
We are missing the weird bit where somehow the knowledge to make Ballistic weapons are gone/lost to the majority. Also the area of space they are in now has so much bs in it that both long range communications and lasers are worthless.
This manga is going at breakneck speeds. The 'chapters' aren't very long, but we went through like 4 chapters in 4 pages. The Maria bit takes most of 2 chapters, and allowed more infodumps. Also pretty sure whatever declaration here doesn't really have someone overhear it if it existed. Makes me a bit worried since we are speeding through other slow bits when most of the first volume is the slow bits.
We are also missing quite a bit of Nao's internal dialogue, which tells us that while he is a death seeker, he will do everything he can to prevent other people from dying to his wish. Hence why he keeps thinking about captain's going down with their ship or heroic last stands, like Gandalf preventing the Balrog from chasing the group. Which is why him being thrown into any officer capacity is terrible for his dream.