Rejection only means what you make it mean and only has the power you give it. A person who response, "No, I'm not interested" is just that—not interested, by whatever criteria they have set up to qualify as "interesting". And god knows what that might be.
This expression of non-interest has nothing to do with your value or worth, unless you yourself choose it to give it that meaning and allow it to have power over you to affect your emotions. If you choose to let the experience of rejection be a confirmation of your own sense of unworthiness or low-self esteem, that is something you do to yourself.
Frankly, the person who rejects you doesn't know you well enough to be truly rejecting the real you, so don't give it any more weight than necessary. More often than not, they are rejecting what they perceive as you, which more often than not, is inaccurate.
Don't let your emotions get the better of you. Know the reality of what is really happening. This is true character—being able to discern what is true and what is not, what is helpful and what is not, and what you should give power to or not. You're in control of your emotions. Not them.
As long as you are true to who you are—"pretty nice guy"—then I don't see a problem with you finding a person who resonates with your spirit and person.