what would you do?

what would you do if you liked this guy and he liked you but he had a girlfriend that he'd been with for 2 years but he was gonna break up with her and you went to see him had a few drinks then started making out? would you tell him to choose between you and her? or would you tell him it doesnt fee right and leave the relationship at that?
please help i'm really comfused.
lol.
Tee xXx