You seriously don't need to worry here, m'kay? Even if I didn't generally despise anything more romantic than Scyther/Nightmare (which is, uh, not particularly so), Mark and May are still both twelve years old and way too young to be falling in teh twu wub with anyone at all (I'm looking at you, Phillip Pullman). Alan is kinda borderline, but there isn't exactly anyone left then for him to get fluffy with even assuming he has a slight crush on May, which he might. Unless he were into Poképhilia, and I'll tell you right now that no, he's not.
Even if May weren't twelve years old, had a crush on Alan to some degree and they admitted that to one another and got together in some kind of a relationship, it would definitely be far from fluffy, considering how May has a very bad temper, expresses anger with violence (see elbowing Alan, kicking Lapras, etc), would much rather spend her time battling than watching romantic sunsets, and is generally extremely non-fluffy - she's the type who yells "GET A ROOM!" when people start french kissing in public. Alan would have to consider himself lucky if she occasionally kissed him on the cheek when she was happy after winning a battle. If they got together, this would last about two chapters before they would realize it's not working at all. May is not ready for any kind of intimate relationship. May and Alan can function as friends because she can keep a reasonable distance from him. As a couple, no. He gets on her nerves far too easily, and as I pointed out earlier, she responds to this with physical violence. Not a good recipe for romance, and definitely not fluffy romance.
And even if they were deeply in love enough to make May go suddenly OOC, they have far better things to worry about (such as, oh, saving the world), and if they started wasting their time kissing or getting fluffy, Chaletwo would basically tell them to piss off to some hotel if they're just going to be delaying Mark's important mission. They would never get OOC enough to just say "OMG FINE WE WILL GO AND KISS AND BE FLUFFY IN CLEANWATER CITY WHILE YOU TRY TO SAVE THE WORLD ALONE SOMEHOW :DDD". They'd apologize, stop it, and continue while keeping the romance to any potential times where Mark is not watching (and thus the reader would not hear of it).
So uh. Not gonna happen. Sorry, cakeshippers. As for Mark/May… they are both twelve-year-olds with radically different personalities, no interest in one another and absolutely no chemistry between them. Uh. No. Scyther/Nightmare is plenty enough romance for this fic in my opinion, anyway. :P