Don’t feel guilty.  You did the right thing in telling her the truth the instant you realized your situation had changed.  You did not continue to lead her on or lie to her.  If the roles are reversed, you would want her to tell you right away as well.  Else, it would be even tougher for the truth to come out.

Dating is always gonna be wrought with extreme emotions, but this is the contract we signed when we agreed to be seek someone for love.  It is about finding compatibility, and as long as you are honest with everyone and treat everyone with respect, there is no need to feel guilt.