You might not be aware of this, but since you are a girl I think you are aware that love is transactional. You love someone because that person has something that you want and that person loves you back because you have some thing that he wants. That’s it. If one person is the one wanting and the other person doesn’t want anything to do with other person then there is no love. The first person is just having a crush. The other one has no idea the first person even exists. And the reason your feelings go away is because you first are attracted by the man’s physical features like height, face, look... then you see that the person is socially slow, no other girl is attracted to him, not that rich... just basically nothing is going for him then you loose the attraction. This is what’s happening in that twisted woman brain of yours.