You see, the thing is that James really didn't cause Snape to lose Lily, or Lily to lose Snape. Do you ever remember reading about James in a memory that wasn't Snape's or Voldemort's in the entire series? Every memory we see him in (besides the one where he is being murdered) portrays him as a complete jerk because that's how Snape saw him. I think that James was really just upset that Snape was friends with Lily, that he got good grades, and he also saw him as an easy target to bully.
From the sound of Snape's past, I don't think many people really liked him besides the Slytherins. Who knows? People's opinions of James might have improved because he was, "Teaching Snape a lesson."
We are also continually reminded that in his school days, James was full of himself. But he was still a good guy underneath all of that and he still had true feelings for Lily. He wouldn't have chased her all of those years in school unless he really felt something for her. Snape and Lily wouldn't have stayed friends anyway, because Severus was always running around calling muggleborns mudbloods and he was joining up with all of the wrong people and running around saying he was going to be a death eater and support Voldemort.
They wouldn't have stayed friends anyway, and James became a better person. He had to have become a better person or we wouldn't have heard from all sorts of people throughout the series that he and Lily were good, kind, and honest people. If he hadn't of changed his ways we would have heard about how Lily married beneath her and that it was such a loss that her life was taken from her.
Snape wasn't the best person in the world, we just see him that way now that we know how madly in love with Lily he was. But you have to ask yourself, why would he tell Voldemort about the prophecy he heard? It was obviously referring to the Potters. And when Voldemort said that he was going to murder Harry and his family, Snape only asked him to spare Lily's life. I'm sorry, but that just seems extremely selfish to me. He'd like to save the woman he loved, even though she had a husband who she genuinely loved and cared for, and a son who she carried for nine months and loved more than anything in the world. Snape was a very selfish person and even though he is one of my favorite characters within the whole series, he was just as bad as James, if not worse at times.
I hate to burst your bubble, but I highly doubt that you will find many people who agree with you on this one.
Don't get me wrong though, he did very well after Lily's death by taking care of Harry even though he partially hated him. He was a very loyal man to Dumbledore and he is probably one of the key reasons that Voldemort was able to be brought down. He avenged Lily's death in the end. And he became a wonderful man.
Just don't blame James for everything when the blame CLEARLY falls on Severus' shoulders as well. James really didn't stop them from being friends, it would have happened anyway.