I didn't really 'ship all that much with "Cowboy Bebop". Did Spike and Faye have a thing for each other is a question that gets tossed around a lot. I am 100% certain Faye developed a thing for Spike as the series progressed, but by the time she admitted it to herself, much less him (she never really got the chance to), it was too late. As for Spike, let's be fair, occasionally he flirted back and Shinichiro Watanabe said he did like her, he just wasn't the direct type. If there was never a Julia, or if Spike was capable of letting go of her and his past, then who knows? It would have required a lot of growing up on their part... possibly after a drunken bender was the catalyst, I don't know. But Spike did open up to her at the end, as well as Jet, and I believe what he did at the end was just as much to protect them as it was to avenge Julia. His time had run out and anything else would have just delayed the inevitable, but with worse results. Needless to say, none of this is Julia's fault. Spike is an adult and made his own decisions, which were probably the best decisions given what he knew at the time.
Now, let's talk about the whole "Julia came between Spike and Vicious and turned these good friends against each other" bullshit. Pardon my use of language here, I try to keep that out of essays and rambles like this, but I cannot think of a more apt word: bullshit.
Spike and Vicious were assassins and enforcers in an organized crime syndicate. They were both taken in, groomed, and raised by the Red Dragon capo, Mao Yenrai. According to the guide books, Mao was grooming Spike to eventually lead the Red Dragons, and we know from "The Real Folk Blues" that the elders of the syndicate specifically denied Vicious as their successor. Why? Because Vicious was a predator. The elders and Mao wanted to moderate and work with other syndicates to increase their profits. Vicious killed them because they were "beasts who lost their fangs." Now, just for one moment... imagine dating a guy with a view like that.
While I don't think Vicious was outright abusive to Julia, I can see him easily being neglectful at best. Not to mention, the guy is a creep. Plus there is his implied drug problem (that canister of Bloody Eye on the nightstand was either Julia's, Spike's, or Vicious's... you do the math), and the guy was always something of a nihilistic sociopath. Did Spike and Julia do wrong by carrying on behind his back? Yes. But somehow, I don't think you leave Vicious... Vicious leaves you. How did he react when he found out Spike was planning to fake his death and run off with Julia? He didn't give his blessing, he didn't just gripe about it, hell even just punching Spike in the face and letting it be after that would have been "normal behavior" relative to what he did next. He put a gun to Julia's head and offered her a sadistic choice, either she kill Spike or else both of them get killed. I'm sorry, but there is no "poor Vicious" here. I can buy that he was a "better person" before Spike and Julia dallied around behind his back, but I highly doubt he was ever close to a good man. Besides, when he does confront Spike in "Ballad of Fallen Angels," he doesn't even mention Julia... just that Spike is now a "beast who has lost his fangs" and needs to die. If anything, it was probably Julia who made Spike a better person.
The worst we can honestly say about Julia is that she made a mistake, but this does not make her a slut or a whore or anything like that. Was there a better way to handle this? I don't know... maybe if Vicious wasn't a sociopath, there was. But none of us were the ones in that situation, were we. I don't think it's a stretch to say that Spike was always a better person than Vicious, sure Julia might have awakened that, but the better angels of his nature were always there. If Vicious had any that died when this all went down (and I tend to think he did), I doubt they were ever that strong to begin with. Spike was willing and eager to leave the syndicate for a better, even if far less prosperous life. Was Vicious? The answer is obviously no.