Board Thread:Show-Related Questions and Answers/@comment-5834856-20140423092224/@comment-8345449-20140423102142

OEdystopia wrote: In order to create a bond / relationship with someone, you defenitely need a heart. Removing a heart after this essential bond was build doesn't have such destroying effects because now you you can use your Soul (your volition) to cache it somehow. You felt this emotions and your soul remembers them.

But Graham shared a TLK with Emma that restored his memories so he must have fallen in love with Emma even without a heart.

I would guess in the OUaT universe, a soul is all that is necessary to love but a heart is needed to feel emotions (or at least without a heart, emotions are dulled). If you don't have a heart, you can still fall in love, but because you don't experience the feelings that come with it (e.g. desire, euphoria), you don't realise that you are in love.