I think it is perfectly natural to have wandering thoughts like this when you fancy someone. I would say if it doesn't go so far as to interfere with actual interaction with people that it's not so bad. A daydream is nice now and then. It may be true that it's simply an infatuation, but there is always the prospect of that turning into something more. I would say the only time these future thoughts would be a real problem is if you put too much pressure on the relationship because of them or didn't allow yourself to be fully in the present. It's all well and good to think about what may be (perhaps you will manifest it...) but just don't forget to enjoy what is!
I am sure others will have another take on this.