It's okay to have infatuations and daydreams, as a previous poster suggested. No harm no foul!
Just remember that it takes months of intimate conversation and interaction to really get to know someone. Over time, your daydreams of a person will be replaced by the reality of that person. You may want to remind yourself that your infatuations are based upon assumptions, and that assumptions change.
In other words, you don't build a house before checking to make sure the soil can support it. Likewise, you wouldn't want to get married before you are sure the relationship can sustain it.
But that doesn't mean you can't daydream or be hopeful! Of course you can!