Robin was going on a walk until he found the entrance that led to the bridge between Earth and the underworld, there he met the love of his life and the little sister of 'Raven of the underworld'. What they didn't know was that deep down in their hearts, they were actually soulmates, that day was the day they were meant to become lovers.
I got the idea for the whole 'soulmate' thing from one of the miraculous soulmate Au videos I watched. So if you were to watch one of them, you would see where I got the eye color soulmate attribute idea from. Also quick shout-out to Monay Brown. You are a big sweetheart Monay Brown.