How does it feel to actually be 'in love' ?

Do those of you in successful long term relationships actually know what it feels like to NOT be in love and feel 'emotionally empty' because you don't have a positive rewarding relationship?

I used to think I knew what 'love' was (in an adult romantic/intimate sense), but I don't think I actually do and I've just 'given the impression' because all I could do was 'fake it until you make it'. sigh.