Apart Together
They can't be together. They know this. They know the risk. Being together, close enough to touch leads to the temptation to touch. Touching leads to the temptation to kiss. Kissing leads to the temptation to…no, the risk is too great. So they agree that they must be apart.
But they can't be apart either. They know this as well. What to do? Can't be together, can't be apart. So they take turns watching each other. They both know they do it, but it's better than the alternative…being apart.
Buffy has to go to LA every second weekend anyway to visit her father. Only she ends up spending most of her time shadowing Angel.
Angel needs time off anyway from "saving the world". His mini vacations always take him to one place…Sunnydale where he watches her from the shadows. She can always feel his presence, like an amputee feels their missing limb. But she pretends she doesn't know he's there because knowing would lead to seeing which would lead to touching then kissing then…the risk is too great. Better apart, together.