Man, if it turns out to be Will/Liz, Liz is a horrible girlfriend. She doesn't ask Will anything about meeting his dad, she never makes him feel special, she technically cheated on him....and she never says she loves him to him. She says to Jack she loves Will.
"I've come to find the man I love."
This sounds more like trying to give Jack a guilt trip than an actual confirmation. "I'm here to find Will" would have worked just as well, and granted, she does look concerned about Will when she says, "Jack, I know Will came to find you. Where is he?" And by his face, he takes her seriously. But why tell Jack? Why not tell Will to his face? He told her and she didn't look all that stunned or touched to me. Maybe it was part of the act, but whatever. She's an emotional girl and she was bound to show emotion if that was the first time Will, or anyone for that matter, told her they loved her.