Ever since FFX came out, right away I saw a resemblance between Cloud/Aerith, and Tidus/Yuna. And there is. They look like carbon-copies even! Both Cloud and Tidus are so much like eachother, and finally, there has been a heroine who looks a bit like Aerith.
Both FFVII and FFX are similar in each and every way..more than most of the other FF games. Cloud agreed to be Aerith's bodyguard, as Tidus agreed to be Yuna's guardian. Both Cloud and Tidus appear to have feelings for Aerith and Yuna, but aren't sure how to really express it. In the ending of FFVII, Cloud tries to reach for Aerith's hand, in which is the last time he sees her. In the ending of FFX, Tidus hugs Yuna before he disappears.
Cloud wasn't ready to react to everything Aerith did, because he has never had that "experience." As Yuna didn't, she wan't ready to react to Tidus's mixed feelings. They both seem to have the closest relationship, compared to the others in the both games. And obviously, have mutual feelings for eachother, but are unable to express it into something more before Aerith and Tidus reach their demise.
In FFX-2, we can tell Yuna is still inlove with Tidus, and attempts to search for him. As in other games following FFVII, Cloud seems to be lingering around many places, in hopes to still find Aerith.