I think that, ultimately, the blame for the break-up of Riley and Buffy has to be shared equally between the two. Both entered into the relationship wanting something that the other person simply couldn't give.
Let's start with Buffy. She had just left, or had taken from her, a relationship that was doomed from the beginning. She is the Slayer, Angel, soul or no soul, is a vampire. Sworn mortal enemies. To make it even worse, if they manage to overcome their differences and consummate their relationship, world destruction is narrowly avoided. Be that as it may, up until that time, Angel was the closest thing to a match, at least physically, that Buffy had ever known. But Angel, under very heart wrenching circumstances, decides to head for the bright lights and big city, putting Buffy and the temptation that she represented, behind him, at the end of Season 3. No surprise, Buffy, a normal, hot blooded young lady, decides the next year that what she needs is a normal, HUMAN boyfriend to snuggle with (I'm gonna skip Parker for the moment, but, rest assured, he will return momentarily) Enter Riley Fin, Iowa farm bot and assistant to Professor Maggie Walsh. Tall, handsome, friendly, very obviously interested, and, best of all, a normal human boy (this is before the big reveal in "Hush") Everything that Buffy could wish for, summed up in one single statement. "He's nothing like Angel." No superhuman powers, and no breakaway soul. Even after "Hush," Buffy is still working under the assumption that Riley is just a normal, if highly trained, human, with no chemical or electronic enhancements. Just what she wants. A normal boyfriend, and even better, one who could go Slaying with her.
And now, we look at Riley. Highly trained, supremely motivated. Dedicated. Devoted. All that he can be. Maggie Walsh's favorite assistant, and no doubt reminded of that by both her and his fellow commando's. Along comes this sweet, rather lost appearing blond freshman, obviously in need of a protector. Just look at how she fell for Jerko Parker's line (I told you that he would be back) Somebody like that definitely needs protecting, and Riley Finn has the perfect wing to tuck her under. Even after "Hush," he still thinks that, super strength and accelerated healing aside, he may not be her equal, but he's awful close, and, with a bit more training and experience, he's gonna get there, sooner or later. (Elite fighting forces, whether Army Special Forces, Marine Force Recon, or Navy Seals, instill that in their members.) Time goes by, and, not only does Riley NOT get closer to being Buffy's equal and protector, without his chip and mega-vitamins, he actually becomes LESS powerful than before. Riley is no longer all that he could be, he's less that he used to be. Dissatisfaction and bitterness ensues. He begins to become more and more demanding of Buffy's time, time that she doesn't have to give, and when he doesn't get it, he goes to someone who WILL give him time.
Buffy wanted Riley to be her normal, human, boyfriend, who just happened to be a demon fighter in his own right, and he wanted to be more than that. Unfortunately, he just wasn't capable of doing it.
Riley wanted Buffy to not only trust him as a lover and respect him as a fighter, but also to be looked upon as her defender and protector. Unfortunately, she couldn't do that.
Both Riley and Buffy entered into their relationship, or at least discovered it quickly thereafter, that what they had each wanted from the other just wasn't really there. To give both of them credit for the effort, both Buffy and Riley tried to fit into each other's life and to include them in their own, but, ultimately, it just didn't work out. Luckily for both, their affair ended with only pain and regret, not tragedy, death, and disaster. To Riley's credit, he did finally come to the same decision as Angel, if for completely different reasons. Neither man, because of either a cursed soul or physical and emotional incompatibilities, could give Buffy what she really needed when they were together. Only one man would ever be able to give Buffy everything that she would ever really need, and, though she had met him by that time, she had yet to see just what his potentials really were. That would come a couple of years later.
But that's a discussion for another thread.
But I will say this. I ain't talking about Parker.
