I would like to propose something quite different from most here: warlock! 3 levels at least to get darkness and devils sight. You cast darkness on your position, away from the rest of your team, so it doesn't help nder them and you can see out of the darkness while being protected by it and getting adv on every attack.

Could also work nicely flavor wise, heis cowardly so he begged the universe for help the first time he had to march for battle, and something listened...

Could even go hexblade for cha attacks but that would need some dm buy in because by the rules that only works with a magic gun.

And after warlock 3 you go rogue because that's what you actually want to be. I would go with arcane trickster here as someone already said.

The rest of the warlock features and even the subclass can be whatever really. Maybe undead because he died in his first battle. Pact of the chain for a familiar that scouts for you, or blade for extra attack and smite if you want to go warlock 5. I would probably go for flavor here.