Cloud might not be in love with any of them. He was obviously infatuated with Tifa from a young age, but given the fact that there was what, just Tifa and maybe one other girl in the village, it is highly likely that his affection was one-part genuine and one-part forced. Humans tend to seek companionship like that, from what I understand. (I read this great thing once and I have no idea so forgive my poorly executed explanation.)

He probably had a thing for Aerith, but that would have been influenced by the strange sense of familiarity courtesy of Zack, the fact that he was her "bodyguard," and the fact that she seemed to be a bit flirty with him. (Aerith was probably attracted to him because of his muscles, his excellent hair, and the fact that he reminded her a lot of Zack.)

As the game progresses, the party has to deal with a lot of trout. This heightened sense of danger and all that adrenaline creates super powerful bonds between people and probably emphasised the "feelings" that Cloud had toward anyone. Spending that much time with them anyway would've probably resulted in that; I'm sure a lot of you would have felt crazy infatuated with someone at your school and then the feeling kind of fades once you no longer have to see people (if that doesn't work for you: how many of your highschool friends do you keep in contact with?).

Prior to defeating Sephiroth, Tifa has all the attention. I mean, Aerith is out of the picture sure, but she opens up about her feelings (genuine, or as above) and depending on your dating score, they might do it on the grass. That doesn't necessarily mean there's anything romantic (could be just getting pumped up for the big day), but between Tifa admitting feelings and Cloud's gratitude at her helping his mentalness subside and the feelings from his youth, there's a strong argument for them being romantically involved.

Post Sephiroth though, Cloud loses his trout and gets hyper depressed. There's nothing pushing him forward any more (I don't mean JENOVA cells), so all that adrenaline falls away and he gets angsty at failing his one job in protecting Aerith. That doesn't necessarily mean he is romantically attuned to Aerith, only the guilt over letting a friend die.

The kicker is that he leaves Tifa and the kids. He takes this protective role, and it's a pseudo-family, but then he gets complacent or whatever, and has to get out. It could be primarily caused by the guilt, or maybe his feelings weren't strong enough.

Spooniest is probably fairly accurate with his post up a bit further, but yeah, I don't think Cloud necessarily loves any of them, but at the same time, maybe he loves (romantically) both Tifa and Aerith, or maybe just one or the other. It's hard to say.