Their relationship was always a constant struggle despite their feelings. When they finally consummated their love for each other (on Buffy’s 17th birthday) Angel’s soul was taken from him (due to a curse-clause; if he achieved true happiness he would lose his soul) and Buffy was left with a vicious killer where her loving soul mate had once been. He proceeded to torment her and attack the people she loved. Buffy discovered that Giles’s girlfriend, the computer science teacher at Sunnydale High (also a techno pagan), Jenny Calendar, had been sent to Sunnydale as a representative of the Gypsy clan that had first cursed Angel. Buffy confronted her and told her to curse him again. Miss Calendar told her that it was impossible because the magics that had been used to curse him the first time were long lost to her people; they had no way of translating the texts.

Eventually, using a computer program she was able to translate the text to English. Before she could tell anyone Angel killed her, smashed her computer, and burned the printed version of the curse. The only copy of the curse that remained was saved on a disk and had fallen behind the desk. The disk was later discovered by Buffy and Willow. Due to Angel’s most recent plot at the time (it involved awakening the demon Acathla and opening a vortex that would suck the world into hell) they attempted to curse him again. The attempt failed when a group of Angel’s minions attacked. The attack resulted in Giles’s kidnapping, Willow’s hospitalization, and the death of Kendra (the other vampire slayer activated after Buffy's drowning). Buffy went to fight Angel one final time (with the help of her new found ally Spike—he hated Angel and wanted his girlfriend Drusilla back so was willing to help Buffy stop him).

They were in the middle of a sword fight to the death when Willow attempted the curse again (little to Buffy’s knowledge). Right before Buffy was about to kill Angel and avert yet another apocalypse, the curse succeeded and Angel, once again, regained his soul. The problem is Angel had already begun his ritual to awaken Acathla and end the world; the only way for Buffy to stop it at that point was “one blow [that] [would] send 'em both back to Hell”. Angel’s memory of the things that he had done had not returned yet so he had no idea what was going on. So “[Buffy] told him that [she] loved him, and [she] kissed him, and [she] killed him”… or so she thought she had killed him. Angel was not truly dead, just in a hell dimension.

Angel returned the following year (as far as we know, brought back by The First Evil in hopes that he would turn evil again and kill Buffy) and Buffy nursed him back to health. They made a few vain attempts at having a normal relationship after that but eventually Angel tells her that the relationship isn’t fair to Buffy. He would never be able to give her children, grow old with her, make love to her (due to the curse-clause), etc. because he’s a vampire. Angel told Buffy of his plans to leave town after they fought the Mayor (season 3’s “big bad”). Before he got a chance to leave he was shot with a poison arrow by Faith (the rouge slayer who had teamed up with the mayor). In order for Angel to be cured he needed to drink the blood of a slayer. Buffy went to fight Faith and attempted to kill her in order to cure Angel but fails; Faith was stabbed but jumped from the building into the back of a truck and escaped Buffy.

Despite Angel’s initial resistance, Buffy, refusing to give up and let her lover die, forced him to drink her blood (a very cool dramatic scene). After all was said and done and killed, Angel left town and moved to LA (he got his own spin-off show at this point). Buffy and Angel have seen each other a few times since then, one of the most recent times being at the funeral of Buffy’s mother Joyce; Angel went, after dark, to the graveyard where Buffy was, to comfort her. They shared a kiss but Angel soon had to leave again. After Buffy’s death and resurrection Angel and Buffy met once again (off-screen) but we weren’t told much about what happened during the meeting; from Buffy’s mood when she got back we’re led to believe it wasn’t a happy, pleasant one. They didn't meet again until the final episode of Buffy in which they kissed.

They talked about her relationship with Spike and the possibilities of a future for Buffy. Buffy told Angel that sometimes she thinks about her future and insinuates that she could picture herself with him someday but it would be a long time coming. She expressed a desire to find herself first before she focused on romance. Angel replied "I'm not getting any older."