It's perfectly possible for Rey to end up single. And I'm pretty sure that's the case, as FinnRose seems to be the romance of this trilogy, not Reylo.
My personal opinion is that whatever happens between Rey and Kylo will be ‘so much bigger’ (quoting Luke from the trailer) and much more complex than them simply falling in love and flying off into the sunset on the Millenium Falcon.
Given what we know about what might go down on Ach To, it seems like Rey and Kylo might fit into the ‘Adam and Eve’ archetypes as they seem to be expanding knowledge of Force lore and ‘upgrading’ the idea of the Jedi. Finnrose feels like a traditional type of romance that could bring some lightheartedness to an otherwise seemingly 'dark’ movie. Reylo is dramatic, complicated and both characters have massive obstacles to overcome but that doesn’t mean it won’t and can’t happen. It’s just a different kind of story. I think the resolving of the conflict between Rey and Kylo Ren and their union will be symbolic of the Force balancing itself out as they are both embodying the dark and light sides of the Force, so it’s already something very different from Finnrose.