By the end of season 4, you can actually see that they both like each other a bit. In season 5 it's even pointed out. Patrick knows that Teresa has a weak spot for him and he uses this to his advantage. She has almost lost her job multiple times for him and can seemingly refuse him nothing, going along with all of his plans.
Patrick is really cruel in that way, using her feelings for his own gain regardless of what it does to her. Now I understand why Lisbon was so angry in season 6. He really can be manipulative and cruel.
Lisbon gives him a chance to own up to his feelings way before season 7. He could have done it right there in season 4, but of course he didn't. It's obvious she cares about him a lot as when he was gone for 6 months she couldn't even sleep at night over him. In a sense I wonder how she could love someone so manipulative and cruel. I don't know if I could.
