The last words from Priceline by the OP: "Your airline has notified us of a schedule change not reflected on our website and we need to review alternative flight options with you."
It seems that Priceline has made an offer to review the possibilities. Why is this treated as an outrage unless one finds out what the alternatives they offer are? I assume that the OP and SO want to get from A to B. Whether or not they are on the exact same flights should not be the issue if they can leave and arrive within a reasonable interval of one another.
+1
Is there a compelling medical or other tangible reason for wanting to be on the same flight as the SO? If not, then the fact that the bookings are separate, stand-alone bookings means that you assumed
some level of risk that you and the SO might have your travel plans disrupted. I know that travelling separately can be stressful, however, isn't reaching the destinaion more important than who accompanies you on the airplane?
I don't mean to say that Priceline is in any way absolved of their responsibility to get you to your destination very close to your original scheduled arrival time - they are VERY MUCH responsible to do that (or to refund your money if they cannot do so).