It is clear that Angel was bonded to Darla - even when Darla was wholly owned by The Master. It was only when she almost killed Joyce & tried to kill Buffy that Angel hesitantly killed her.
Angel even tried to stay with Darla after her got his soul, until *she* rejected his human 'weakness.'
Angelus was bonded to Darla. He gave up his life as Liam for her. He became the monster she wanted. He followed her obsessively for hundreds of years through multiple abandonments.
Neither attachment was remotely healthy but it is Darla, not Buffy whom Angel was prepared to die for in the trials.
He nearly got his whole team killed in his obsession over Darla.
When Buffy was scheduled to die at the hands of the Master, Angel went off to mourn and feel sorry for himself. He did not take any initiative to go fight by her side.
- It was Giles who was prepared to go and die in her place until Buffy stopped him.
- It was untrained, physically weak Xander who had the balls to go up against TWO master vampires (Angel AND The Master) in order to save Buffy in the Master's lair. Xander saved her. Given the opening hellmouth, it is likely Xander saved the world by saving Buffy.
Angel experienced the bliss of someone truly LOVING HIM. At no other time did anyone love him the way Buffy did. I do believe that was a trancendent experience.
Yet when he lost his soul, he could not love her at all because his love was transactional. Only valid with the soul. And yet when the soul came back, he still left instead of trying ANYTHING to try to keep his soul.
He could not give up being a vampire to be with her. He had one day as a human and it was too much weakness for him. He threw it back even though being human was what he said he wanted and Buffy was overjoyed to have human Angel. He had the Riley problem. He could not handle being a 'mere' human.
I don't believe he loved her back. True love requires sacrifice. He cared. He felt loved. Not the same as loving which requires doing FOR your loved one. Love is more than a feeling. Love is an action.
Love is dying for your sister and the world.
Love is dying for the woman you love and the world.
Buffy's love was a unique experience, but not enough to capture the whole (Angelus as well) person.
His father rejected him. For centuries he carried the wound that he would never please father. I think he did not attach well because he was not allowed to attach to his parents.
Darla rejected him when he got the soul and abandoned him repeatedly over the years whenever he became inconvenient. Yet he kept caring about her.
I don't believe Angel had normal "attachment" to anyone. The closest was Darla. Even that was very obsessional.
I dont believe Angel or Liam or Angelus had true love. I believe that the strongest bond he had was to Darla.