And I just have to say, wow, how manipulative were those claddagh rings?
Angel's about to leave town for months or longer - and Buffy's right, he could quite possibly be killed. And if he was, she might never know. And what does he do? He gives her a ring that represents devotion, and wears one himself. Buffy's a teenager who is head-over-heels with her first love. Angel's nothing of the sort. He spent his adolescence and young adulthood leading women on with false promises in order to get sex out of them. He knows how to manipulate immature women. He wants Buffy for her heart, not just to sleep with, but he also must know that teenagers can move on from love in the course of six months to a year. He's previously indicated that he believes it would be in Buffy's best interests to do so. But when it comes down to it, he makes an incredibly manipulative move to discourage Buffy from moving on.
Note that when Oz leaves Willow for an unknown period of time in S4, he doesn't ask her to wait from him. He hopes she will, but he doesn't expect her to. Willow's an adult who is old enough to understand the implications of that kind of commitment, and Oz doesn't have much experience over her. Buffy's a kid. Angel doesn't make his request upfront, either. Instead, he manipulates her with talk of "devotion" and beautiful rings. The kind of thing that a naïve child would fall for.
So, yeah, this is part of why Angel pisses me off so much in The Prom. Buffy is finally a legal adult, graduating high school, becoming worldly and responsible, and now you leave her for her own good? Seriously?