The thing is Natsu is too oblivious to be in a relationship but gray on the other hand (for example) isn't. He isn't into Juvia and we don't really know who he likes.
I think that in the future natsu and Lucy will be married happily. But sometime I think of lissana who made a promise to natsu to get married.Though I am very confident that natsu and Lucy will be together. Gray likes Lucy a bit though.
Nalu, yes as I know they got together in the Манга *spoiler* anyways in the future they will be receiving a daughter named Nashi and speaking of Nalu, Gruvia will also happen by the way Juvia and Gray will receive a son named Storm who will apparently like Nashi in the dear future so exited to see the kids and ships but also DA FIGHTING, so yes it has a huge possibility
