Cool, sounds like it's not as bad as you were painting.
If your buddy has an old 250 (assuming Rebel, late 80s like there are SO many of out there, they last forever and have taught millions of people!) around just as a 'backup', why not see if you can make a deal with him?
Unless his bike is shit, doesn't really
need a backup, and it would likely be perfect for you to learn on for a season or two. With my random assumptions about brand and age, seems like $1000 or would be a fair price (more or less depending on if it's newer than 1990, or in rough shape, etc). Seems like those are selling for $1000-1500 pretty constantly, see what you can do. If he's letting you borrow it anyway, I'd see if I could swing a deal there. Depending on his own money situation and how friendly you are, maybe could even work it as a "half now, half in a couple months" deal so you can pay it off in a couple chunks? that gives you something that's yours, and available all the time vice having to go visit and have him around. Gets the bike out of his garage, doesn't have to take care of it, and if he's letting you ride it around and take the risk of dropping it, you might as well own the risk of loss to value.
When I was starting, most of my rides were of the 15-20 minute variety anyway. Hop on after work, drive a mile down a empty back road, and then do a few laps in a parking lot. Small, slow stuff to build up some confidence. And stay the hell away from traffic, multiple lanes, intersections, etc. Gotta be able to handle it yourself before you toss in unpredictable variables! First time out on the roads after, I was doing fine myself, but a van pulled out in front of me and I almost went right into the side of him.
Like I said, you do better when you assume that EVERY car is actively trying to harm you. If there's a car on a side street, assume they're about to pull out. Stopped at a stop light? Keep it in first gear (with the clutch in, obviously) assuming the guy approaching from behind isn't paying attention. Every car you drive by in multiple lanes is either drifting around and texting or just doesn't see you and about to merge into you and your lane, so either hang back or accelerate past them quickly before settling back down to cruising speed. Pot holes you can't see are about to eat your front tire and fling you forward. Every time you're slowing down, don't just put your brakes on, pulse them a couple times in the process so the light flashes before it goes solid to get attention.
It's a little bit of a crazy mentality, but IMO really how you ought to be riding. Most of those things won't happen, but more often than you'd prefer, you'll notice at least one of them. If you don't get too zoned out and relaxed and actively scan for those sorts of things and take action upfront to avoid them, you'll be a lot better prepared for the quick braking, acceleration, or swerving you need to keep the shiny side of the bike up.