This is all speculation but the stars are starting to align. Neither of them are in a serious relationship and have incredible on screen and they are saying some amazing things about each other.
Mandy says about him:
"He’s such a special guy, it’s really not hard to have to just love him. I feel very safe. I feel very, like, protected with him… I’ve never really felt that with somebody I’ve worked with before."
Milo Ventimiglia said that he "loves Mandy very deeply" which is so what his character WOULD say. They would be a perfect pair!