One possibility here is that this situation helps reflect on your own karma pertaining to love. For example, did you fear this person may not enter a permanent partnership with you, therefore you did not ask for this, even after sex or other good events? Maybe the other person was confused by this.
Furthermore, this can be a test of confidence for how you view your relationships. You said you thought everything was going well. Maybe you need to simply persevere, or maybe you have to rethink your actions and perceptions, not just towards this person, but love overall.
How did this event make you feel overall? Do you feel that you as a person or lover are shaken, or do you this as just a problem pertaining to magic?
As JG Karnonnos also asked, what did you affirm here? Maybe they do love you, in accordance with your affirmation, but if you did not intend for a permanent relationship, then this was one result. It doesn't mean it was a total failure, though.