Well it fits in with the themes "Pure Heart" and "Locked Heart/Anxious Heart" doesn'it?
Well I think Aerith was symbolised in Advent Children with Light and Water what with the random flashes between "light" Aerith (Aerith praying, sunbeams in Aerith's church, etc) and "dark" Sephiroth, and of course Aerith''s holy light materia jesus cleansing water of healing
Especially with "Water" I think they were even going to have/originally had a music theme called funnily enough "Water" lined up for the movie as well, dunno what happened to that/there
There's also this statue, with the light in Aerith's church, dunno/can't remember if it's official or not though -
http://kotaku.com/5127134/a-sulky-expensive-cloud-strife-statue
**
Cloud loves Aerith in the same way he loves Zack!
Seriously though both of their deaths affected Cloud deeply even if he doesn't always show it straight away -
Cloud
"That's why I should quit this journey."
"Before I do something terrible."
(He raises one fist. He is shaking.)
"Cloud
"But I am going."
"He destroyed my hometown five years ago, killed Aerith, and is
now trying to destroy the Planet. I'll never forgive... Sephiroth."
(He stops shaking but does not lower his fist.)
Cloud
"I... I must go on."
He mentions Aerith here, what Sephiroth did to her mattered to him. Cloud didn't get over anything, it's not just Aerith but she was part of it, but what happened in the Black Materia/puzzle room the Temple of the Ancients, what happened with Aerith outside of the Temple of the Ancients with the break down he had, and the whole City of the Ancients Arc from Cloud trying to chase after Aerith in the Sleeping Forest to him freaking out at the altar, Cloud was barely holding it together "that's why I should quit this journey, before I do something terrible" even as he tries to pull it together and states his resolve to follow Sephiroth (and as we all know he was being led the whole time) he;s shaking and still struggling to hold it all together, that's why he asks the others a favour, to come with him/promise to save him from doing something terrible. Cloud was ready to shatter and the whole Cloud you are a clone thing/illussion of Nibelheim with Sephiroth and Tifa, with Sephiroth taunting them and Tifa's memories of Cloud/making out Cloud's past with Tifa wasn't real and Tifa unable to set his mind at ease/sort out the truths from the illussions proper for Cloud to believe (not her fault, she couldn't go in his mind without the lifestream) thing was the last straw. Nobody just "got over" Aerith's death though - it was more they still had a mission to do/planet to save and they didn't have time for grieving at the time. as in Case of Tifa they tried to channel their grief into anger/for resolve to fight Sephiroth.
Of course Aerith/what happened to Aerith mattered to/affected Cloud - I mean "I remember Aerith a lot" and "Memories of Aerith, we've got to set her free" and "An answer from the Planet ... the Promised Land ... I think I can meet/find her there (find in Reminense/FFVII Playback)
*Note I am not specifying romance here though - simply that Aerith was an important person to Cloud/somebody he cared about/remembered a lot =) (obviously he thought about her in the ending, caring about/feeling guilty about what happened to her and he wanted to meet her again for resolution to that, this special/dear friend whom he'd built up a special bond with - remember Square Enix says Cloud and Aerith built up a special bond - so yeah I think it makes sense people thinking they were dear/special friends
(and no though they weren't "friends with benefits" though sorry! )
*And I was going to dig in/get more into the ins and outs of main heroines/love interests and the difference between them again and what the official stuffs say but now I can't be assed
*goes to bed* *yawn* ^-^