When was the last time we say Angel was in Buffy?

In the last two episodes. He came in "End of Days" for the last few seconds and kisses Buffy. That episode ends and he is in "Chosen" for the first few minutes until Buffy tells him to go and fight his own fight.

definitely Chosen. Last episode of Buffy, last time Angel made an appearance in that show.

Angel WILL EVER BE in Buffy, 'cause he's inside of her since he has been her first love and lover. The development of Buffy throughout the series is deeply intertwined with the relationship she had in her life, all of them less or more building on her personality (yeah, even that Parker scumbag).