I think that as you are only 22 you need not worry too much about finding the perfect husband just yet. There's no hurry! And it's certainly not a defining objective for a girl these days.
If you are not happy with Rick then that would seem to be enough to me to end the relationship. I would be wary of ending something good because you are hankering after something new though (Paul). How do you think you would feel about Rick if Paul disappeared tomorrow?
If you have doubts about the relationship and your ties are not that strong nor serious, then you should leave. Think that the more time you stay together, the more it hurts when it's over. Talk to him and express your feelings and walk away as graciously as you can.
Your not happy. Your not a bad person because you feel this way. Your young and not married this is the best time to find your self. Don't rush into marriage because he is a good guy. You will be doing both of you a disservice by getting married to someone you are not in love with. I say take abreak and re-evalute what you want. I think you still want to play around a little. So stop dragging him along and move on.
I think you should let him down easy however you also need to be more honest with yourself. It sounds like you want to break this off because your crush is better for you et al. It also means that you again are jumping into another relationship and leaving your current bf holding the bag.