I hate it when people interpret that one scene, saying they had sex. they didnt.
1. If they had sex, why didnt they have babies? Also, dont say condoms due to the fact that condoms dont exist in the FF world and because cloud doesnt carry condoms even if they did.
2. the terrain was rocky and mountainous, making sex inappropriate and uncomfortable
3.cloud was in love with Aerith, who he knows always watches him, even after her death. Remember, he knew that she did not go to the promised land because her spirit was still attached to the world.