You're over-committing to this person. It's like if someone tried to give you something valuable for free- you would feel like something was wrong with it wouldn't you?
It's human instinct for girls to avoid men who come easily. Douchebags are douchebags, because they don't limit themselves to one girl, they will hit on multiple, multiple girls until they strike lucky with one and move on.
In other words, you can still be a nice guy, but don't be needy. If she doesn't offer the same rapport back, move on.