I agree with so much of what you said. I think why Roger didn't immediately go to River Run with Jamie and Claire is one of the things that most fans misunderstood, and that drives me bonkers! So many people have criticized Roger for taking so long to decide and ask why he could ride along side Jamie and Claire while he thought about things.
I think most people are forgetting that Roger isn't trying to decide whether or not he can still love Bree or raise a child that isn't his. He's wondering if he can accept living in the 18th century indefinitely and possible forever. River Run is in one direction, and the stones that Roger found are in a completely different direction. If Roger starts traveling with Jamie and Claire, he'll be going away from the stones. While Jamie was being a bit of a baby/bully when speaking to Roger, he wasn't entirely wrong (and Claire said it better). If Roger isn't prepared to be a husband to Bree and a father to Jemmy and live in the 18th Century, it's better that he go now rather than get Bree's hopes up by going to River Run, only to break her heart again and leave. They made it clear that Roger needs to not come to River Run unless he had decided to stay. If he isn't ready to turn his back on the stones (possibly forever), he needs to wait until he is.
I do disagree that Roger is responsible for the 2 deaths. That situation was already in motion, and I don't think Roger did anything to influence the outcome. Maybe by fueling the fire the girlfriend found it easier to join the priest on the fire, but I suspect she would have done that at some point. If I remember correctly from the book (and it's been awhile), Roger had nothing to do with that story other than be an ear for the priest while he was in the hut.