well, this man may be cheap, what is done, it is done, move on.
for the future, if you date Americans again, and do the "go dutch" thing again, just make it simple, 1) you can either just get a sepeate check for yourself and pay for your own tab and tip.
2) if you get just one check, then jsut add 15% to 20% tip to the total or more, if you are happy with the services, and then round it up, each pays half. As who orders more expensive dish, or drink, best not to be so niclking and dimding. jsut split the total bill (with tip added).
Many Americans don't have good math.make it simple.