well even without a multiverse DC still published Elseworlds line, so having only one earth wasn't a block to write about a multiverse. DC on Flashpoint keep it a multiverse, at least this they really learned but DC just getting their continuity more and more confuse/convoluted
so why have the two character dating if it isn't important? with the focus on wonder woman a mention could be made, then Johns choose to expose what her feels about ttrevor