The Heart icon represents your couple’s presence.

If it’s red, it means that your couple is playing.

If it’s gray, your couple is not logged-in.

If the Heart icon shines, it means you can call your couple to your location; simply click the icon to call your couple and the message (with appearance of love message) will be sent to your couple.

To know more about the couple system, follow this link: http://sealonline.wikia.com/wiki/Couples