Tell her to leave Jeff’s place and come over.

“How about this,” you say. “You spend your day with me instead of Jeff.” You smile at your own boldness.

“I really shouldn’t. Jeff will be really upset at me if I bail on him.”

You roll your eyes. He really has her wrapped around his finger.

“I’m not asking what Jeff wants. I’m asking Tina what she wants.”

There’s a long pause. The kind of pause that makes things clearer the longer it goes. The kind of hesitation that says a lot. Not everything, but a lot.

“I can’t.”

She’s not denying it. She probably wants to come over, at least on a subconscious level. You could try to manipulate her into coming over with your silver tongue, or you could give in and be a gentleman by going to Jeff’s place.