Stop and take a deep breath.
First and to solve your problem, call a local cabinet shop. Ask if they know of any one that rents time on a wide belt sander.
My local guy charges $80 per hour with a ½ hour minimum. I've never been able to accumulate enough material that went over the ½ hour. From your description of the problems it sounds as though you are well over the $40 in sandpaper alone. Allow your guy to sand both surfaces as it will make it easier to finish the underside of the table top. Pay the guy in cash. His wife/girl friend will love it when he takes her out for dinner. (The cash goes into his pocket and not into the accounting system.)
When you use the final wide belt it probably be to 120 grit. You could do 180 grit if you are going to stain or 220 grit if just polyurethane. Regardless do some sanding on the end grain to 400 or 600 grit. That way the ends of the table will look the same as the top after staining.
With machined lumber I can not imagine using 80 grit. If the glue up was that uneven that 40 grit was needed, it would have been better to rip the table top apart and start over with some dowel joinery.
One other comment. A 48 inch wide table is HUGE. It will be exceptionally difficult to reach across during use. Even with kiln dried lumber and used indoors, you can expect ½ inch movement due to changes in ambient humidity. You have to allow for this movement, as a minimum and closer to ¾ inch, when attaching the table top to the supporting frame.
Go back with the belt sander with 80 and 120 grit before you go to the orbital.
I would use my cabinet/card scraper. Love it, don't use much sand paper anymore.
All outstanding suggestions.
I will add some of mine:
A) Your photo shows the 80 grit RO swirls, so as you stated, 120 grit should be your start point if you are going to resolve this yourself.
B) I’ll also point out that if you go to your local cabinet shop, listen to their advice and their 220 grit will easily resolve your swirls in no time.
C) I’ma big fan of General Finishes’ rub-on penetrating oil-polyurethane finishes, and 220 grit is their max suggestion.
D) As with all of our tools, be careful to let the tool do its work, do not force it. This the cause of your swirls coupled with the previous comments about cross-contamination of abrasives when changing grits. Pressing down on the sander guarantees what you now have, so back way off, let the weight of the tool be all that holds it to the workpiece.
E) You can remove the swirls and move straight to finishing with no more sanding if you use a smoothing plane.