Over the years, I've come across several fans who've held vastly different positions on the matter of Buffy Summers' heart. Some see her as never having loved anyone as much as she loved Angel, some see her as loving but never actually being in love. Personally, I see Buffy evolving throughout the series, and just as "Chosen" comes to mean freedom from the loneliness of being the only Slayer, it also means freedom from the trauma and fear that's kept her from truly opening herself up to loving someone again after the horrible pain of her first relationship with Angel.
But what do I mean when I talk about love? Here's how I see it evolving for her over the years.
Buffy loved Angel, there was too much emotion there, too much openness and caring and passion--it's too abiding to call it infatuation. Infatuation would've evaporated at the first signs of strife. It's too abiding to call it anything but love. That's how she felt. But was she in love with him? I don't think she ever really knew him. Cordelia knows Angel and loves him knowing all. Buffy loves Angel before she knows him, and she loves him despite not trusting him (she always emphasizes how she can't trust him even when she's professing her great feelings for him). So Buffy was in love with Angel, but she never really knew him in Season 2, and by Season 3, I think she was in denial of parts of his character in order to continue being with him. This is why Enemies freaks her out so completely.
So if defining being in love means full commitment and what's more, truly intimate knowledge of the person and a completely open heart--then she doesn't have that with Angel. She's in love with her idea of him, not with who he really is. And that's key. I call Buffy's love for Angel a fantasy love.
With Riley, I think she loves him, but she never fully opens up after all the Angel trauma. And I don't mean this on a pure emotional level, but also in terms of intimacy. She does begin to know Riley, sorta, until he ends up becoming a person she doesn't even recognize because his identity is torn apart by the end of Season 4 and he's experiencing an existential crisis in Season 5 with Buffy being the only thing left for him to cling to (which was true even in Season 4--the hankerchief). Buffy keeps secrets from Riley just as Riley keeps secrets from her; they're on their way to getting to know each other in Season 4, just as Riley's losing his entire sense of self--so how can they have intimate knowledge then? They're "Doomed" as their first relationship episode describes them. They don't understand each other, they don't see each other clearly, and so much of their interaction stems from miscommunication and a lack of intimacy. The potential for their love is cut short by them just not being right for each other. They're incompatible.
With Buffy and Spike, they're enemies, they're allies, they're friends, they're sexual partners and mutual abusers, then they become each other's silent strength and emotional reliance. They see "the best and worst" in each other and refuse to look away, but what's more they also help each other move beyond self-deception. Buffy helps Spike see past his own self-loathing with her belief in his redemption, just as Spike helps Buffy rediscover her inner strength in "Touched". They embody love in all its forms: unconditional, inspirational, abiding, enlightening. Clearly, Buffy loves Spike and Spike loves Buffy, but is Buffy in love with Spike?
If I'm defining Buffy's state of being in love as an open heart, a wealth of intimacy and passion, I think the moment that most clearly demonstrates this is in "Chosen" when she says "I love you." This is the first time Buffy is totally present when she first professes her love, declaring her heart of her own volition, to a man in the entirety of the series. Angel instigates the declaration in "Lie To Me", basically waiting for her to emotionally commit herself before he'll talk about Drusilla; and she never manages to actually tell Riley. It's difficult to define commitment when it comes to Buffy and Spike, especially in that moment, but I think she was so caught in this overwhelming tide of emotion that she would've kept holding Spike's hand as the world fell down upon her. She ignores Faith's cries to follow, and she doesn't want to die anymore, but that moment there--I think that's when she's fully in love and loving with an open heart, loving the person she knows, not the person she imagines him to be. Clear eyes and an open heart and a commitment that cannot be shaken by the end of the world -- she's burning with him, alight with love, lost in a world set apart and so painfully true that I feel it goes beyond merely saying she's in love. This isn't just being in love, this is effulgent love, this is transcendent love.
But if that moment is the pinnacle of what it means to be in love, the exquisite embodiment of love in all its lush symbolism with hands that literally burn and a world that literally falls away, it's important to look back to what came before and realize that being in love isn't just about telling the other person or even being with the other person. People can be in love with someone else and not have it reciprocated and the expression of that love can be shown in ways other than words. Buffy shows Spike all the ways she loves in Season 7 (the five languages of love), and it culminates with her verbal declaration in "Chosen", that final barrier to her fully opening her heart again, that damaged, battered organ that's been too afraid to love ever since her father left her, ever since Angel traumatized her in Innocence and the back half of Season 2 and the more in Season 3. In that moment, it's not as if she's suddenly fallen in love, but that she's discovered the clarity and strength to declare it and her love bursts forth, breaking through all those walls she's constructed to defend her heart from pain. Her heart is "full of love," it always has been, and she does not pull away in fear, she embraces love as she grips Spike's hand, and the old wounds are healed with cleansing fire: effulgence of the heart.
For Buffy, love is fire, flame, a fire she wants back, and it's something that grows and grows within her until she's braving the fire to reach out to Spike, trusting him with her heart, so committed to the moment, to the intensity of emotion and love, that she nearly dies with him. Intimacy, passion, commitment all bursting alight, a joining of his heart and hers, a handfasting of soulful flame. If that's not being in love, then I'm not sure what would ever satisfy the definition of "in love" as it's one of the most extravagant expressions of a love "that burns and consumes" that I've ever witnessed in fiction.
[eta] For the record, I love discussing the show and thoughtful discussion, whether you agree with me or not, sends me over the moon. :D