As far as Cloud's feelings for Aerith, I wouldn't neccesarily say love- but I wouldn't put it past him. By the end of the first disk, I think he was so emotionally battered and mentally confused that any romance during that time would have been... disingueous. I have a hard time believing that by the time the entire game ended that he could really love someone in a purely romantic way.
But I think it could have happened. If Aerith were alive, I actually think it would have happened. He was definitely romantically interested in her, and there was a budding relationship between the two. That's the whole tragedy of Aerith, it's a "would have, could have, should have" kind of thing. They could have fallen in love. She would have gone on an airship. She should have seen the entire would. But it's impossible to know, it died before it barely even started.
If he didn't fall in love with her yet, then there would be no way for that relationship to develop. There was only two ways it could have gone. 1. Guilt and tragedy or 2. Accepting it and moving on, with their memory in their heart. He did the first, and by the end of AC/ACC he did the second.
Of course, if a person does think he did fall in love, then I could see him loving beyond the grave as a tragic romance. Just personally though, I couldn't actually see him falling into love or a relationship, fully, until the end of AC- where he finally sorted out himself.
It's not stopping Vincent from loving Lucrecia. XD *imagines him necroing Luci..*
Vincent locked himself in a basement for years so he can feel sorry for himself without interruption, robbing himself of companionship, character growth, and probably many of his emotions.
Cloud's got a best friend (or lover, whatever you wish to think) that he lives with, a job, a responsibility to help rebuild Edge he gladly took up, and a two kids to take care of.
Vincent-Lucrecia mimic Cloud-Aerith a lot, but they aren't the same. I don't think they are suppose to be. Cloud's got a family, emotional support, and friends. Vincent had nothing, or at least he threw away anything he had to mourn. Cloud almost did that, but his situation was different as the things he cherished were alive and ready for him to come back to them.