Your relationship probably started with a love-filled 'Honeymoon' period, but, as your partner's needs and insecurities appeared, they would have started behaving in ways that you found difficult. At the same time they would start finding your behaviour difficult.
To protect yourselves from the hurt and emotional pain of unmet needs you would have closed down your hearts. Unfortunately, although this subdues the negative feelings, it makes it impossible to feel or give love to each other.
This means that you still love each other but cannot feel it anymore.