Does Cloud feel lonely? In AC, the premise of his loneliness is "the happier he is, the more lonely he is." And we know the reason why.
But Cloud's childhood is different from Aerith although from an angle, it looks similar: they dont have friends. Aerith really feels lonely because she want to have friends, she doesnt wanna be seen as a freak girl or even a special one--she wanna be a normal girl like the others. Cloud is someone whose personality is "doesnt want many friends". People with this personality exist in real life, as introvert they can be; I've met several ones and ask an extrovert like me "why do you wanna have many friend?" Cloud is the one who reject the boys because he feels superior towards them, also because he's jealous of them playing with Tifa. Yes, Cloud's inferiority just raises when he failed to be SOLDIER. But, he's like Sephiroth who feels he's special and better than the other. Cloud has a little bit arrogance in him. The journey open up Cloud that having many friends he care for isn't that bad; lowering his ego. As for Aerith, the journey blesses her with many friends care for her she never had before. So no, Cloud doesnt feel what Aerith feels of loneliness. They are opposite. But this doesn't mean he doesnt catch her being lonely few times (heck, even Aerith herself has a speech in Cosmo Canyon) and care for her.
Nah, this is what Aerith JP VA said in CCFF7 Reunion interview: "both Zack and Aerith are similar that behind their bright personality, lies a loneliness they both carry; something that perhaps resonates in Aerith"
"What does I fight for?" People may fail to see how lonely Zack can be because of his bright personality. But Kunsel even catch it, according to one of his email to Zack that he offered Zack to talk to him about everything that wear him down.