Why do we become attached to people who don't text us back right away, won't commit, or are generally inconsistent? Well, in part it’s actually because inconsistency is unfortunately a really powerful conditioning mechanism.
Intermittent reinforcement - that is, when behavior is rewarded only periodically, rather than every time - is effective longer and more difficult to unlearn than continuous reinforcement. When we don't know when to expect something - such as when our partner will call us, validate us, or tell us that they love us - we often work harder for it and can even become more obsessive in our quest to receive it.
But what we're really reacting to is lack, not love.
Be careful when someone is inconsistent with you - it can evolve into a pull more powerful than you might realize.