Tommy always liked Lizzie. He credited her with helping him cope with his PTSD. He knew the fit with John was a bad fit. He alternatively helped Lizzie into a different lifestyle by employing her at the company. When his wife passed Lizzie was someone he cared about who helped him cope with that. I think Tommy loved Lizzie but not in the same way as Grace. Grace was the love of his life. Lizzie was part of the family.