It's sad that Buffy eventually stopped believing that she could ever have that kind of a life, with anyone let alone with Angel. She tried for years to balance her life as the Slayer with her life as the normal girl in the real world. Too much heartache and misery and horrible events and monsters wrecking havoc on her life caused her to give up and just erabrace being alone and destined for a different path than those around her. We saw Angel do this too. Accept that they would never have the marriage and kiRAB and white picket fence. That they would sacrifice themselves to the cause. When she missed the deadline to enroll again in college in AYW she gave up that avenue. We saw her getting on the right path again when she took the job as a Guidance Counselor but things went to Hell again when the WC were destroyed. Angel started to believe he was destined for something with the shanshu and then thought it wasn't even meant for him. He thought he could have something good when Connor was born and then he was taken to a Hell dimension and came back hating him. He took pride in having saved Fred and having that daily reminder that his work is important only to have her body stolen and her soul destroyed.