I'm a bit sceptic when I hear that you don't even have a computer but somehow you're the amazing diver of the bunch. I'm not solo certified, and I don't ever intend to be, but I don't see how it is compatible with renting all of your gear.
It sounds like you're the one breaking your own rules as well: you decided to screw the plan (of sticking with your buddy) in order to not lose sight of the DM. You can't really have it both ways. You can't go for super cheap insta-buddy groups and expect a tier 1 diver. You can't blame everyone else when you're making the same mistakes.
Talk to your buddy pre-dive. Don't be condescending by approaching them and saying "this is how we're going to do things" as they'll just start fighting you on everything. Instead, talk to them, ask what kind of thing they want to do, how close/far they want to be (to you, to the DM, etc), and try to adapt to that. It's also during this discussion that you should try and figure out whether you're compatible.
If you're not, or you don't think you can rely on them, then don't dive. It doesn't matter that you're about to lose the DM if your buddy has an OoA and now you're 20m away, looking in the wrong direction, and now your buddy is fish food, or the other way around. Stay with your buddy.