I think fantasy is fine, but I have found that having an ideal picture in your head of what you want (in a relationship or person) can get in the way of finding something REAL.
If you have a picture of X, Y, Z in your head... you might miss A and B because they don't look like what you want-- but maybe they are something great you never even thought of before.
I am finding in my life that if I focus on wanting a person, or an event to go a certain way-- there's no way it will end up that way and I end up being disappointed just because it doesn't match my fantasy. It's self-sabotage.
begin metaphoric rambling...
It's like going shopping with an idea of a specific item of clothing you're looking for. You may not find it for years, if at all -- it may be out of season, maybe nobody's desigining anything like that... and you might miss some really great items that fit you perfectly because you are so centered on this one idealized, fantasy item.