Within the context of shipping Bangel. The reason I ship them has less to do with me and more to do with the story and the characters. The story and characters feel to me to be larger than life. So I don't believe that for example I feel I ever say to myself, I would love to date a guy like Angel. Angel doesn't exist. Neither does Buffy or Spike. I can't really translate those characters to real life because they exist in this fantasy story world that is very different from my own, if that make sense? So when people make the arguments that Buffy and Angel's relationship is less real than for example her and Spike's relationship I find it kind of funny because really they are all pretty unreal. She is a Slayer, in a supernatural world filled with Vampires and Demons. She faces apocalypses constantly. None of it is real. Not even Riley was "real" he was in a secret Demon fighting government organization. This is different for example from, Friends or even Sex and the City, two other shows in which I have strong Ship feelings for Ross/Rachel & Carrie/Big. So that is the context with which I view Buffy - Fantasy. And in the context of Fantasy I love the idea of this greater love, soulmates, etc, something that I wouldn't be as comfortable with in shows like Friends or Sex and the City - because its more real life stuff.
When I first started watching BTVS I was in high school. So the first time I really became invested in the Buffy/Angel relationship I was less mature about the whole thing. I remember falling in love with my first love and how it felt and those incredibly strong feelings resonated with me. I remember going back and having drinks many many years later with my so called "first love" and it was horrible. He was a total douche. I couldn't believe I had been in love with him as a kid. But as I grew up and kept watching the show it became evident that the reasons I continued to be invested in the b/a relationship were less about my personal relationship experiences, because he was no Angel and I am no Buffy. And by that I mean, I think Angel is an amazing character, an incredible hero and he continues to be amazing as he grows as a character. And also, I, unlike Buffy was not dealing with real life adult situations as a kid. I was not dying, saving the world, killing my boyfriend, fighting evil on a nightly basis. Buffy was not me as a teenager. And as an adult, I get that now. Buffy had incredible burdens, and for the most part she carried those burdens on her own but for short periods of time she was able to unload those burdens onto Angel. She was able to be vulnerable with him in ways she wasn't able to be with others and this extends beyond Seasons 1-3 and into Forever and Chosen. I may not be a vampire slayer, but we all know what it feels like to have the weight of the world on your shoulders and what I do find especially relatable is finding that other person that can understand that burden, you can share that burden with as a true partner.
I do share alot of Buffy's characteristics. I can be a bit neurotic and insecure. I lash out at those I love when I'm hurt. I've said this before, I also went through a period of depression in my early 20s and I had a very similar relationship to the one she had with Spike. And it wasn't all bad, I really did appreciate the Spuffy arc in Season 6 when I got older and basically was like "oh yeah...I've been there." And I even think that the things I went through helped me grow as a person. I can't tell you how much I sympathize with Buffy in Season 6 so much so that its uncomfortable and I don't like to watch. Mainly I don't like the idea that my hero is torn down so much and never built back up but that is a story for another day. So when Buffy went over to Spike in Season 6 and said, "I can't do this" I admired her for making the best decision for herself (something I personally didn't do which would have saved me so much grief). My favorite Spuffy moment (yes its incredible but I do have one!) is in Hells Bells. Buffy looks content with her decision to end things with Spike but it does hurt her to see Spike with another woman. She knows its the right thing to do, to get out of this relationship but she acknowledges that she has feelings for this guy. A weaker person would have fallen back into old habits and continued on with the relationship even when the relationship makes you unhappy. Because I think that even if you are a Vampire Slayer and facing death on a daily basis, you should still try and be with someone that makes you happy.