robin x lewis?

so, today i came across a dialogue that i guess it's a bit rare, when i walked to robin's shop a message poped up her head saying "lew", and what's making this worse is that we don't know who sebastian's dad is, I'm sure u now see where this is going, so do u think he's in a relationship with both marnie and robin and that's why he's keeping them a secret so thay don't know he's cheating on both of them?