This may have been at least partially covered in other threads, but I thought I'd start fresh. Why did Hitch leave town at the end? He left his only friend, and what appeared to be a loyal girl friend (the Russian sounding woman.)
Was it because he pretty much murdered the Jeremy Irons charactor and knew Cole would have to arrest him?
My take is close but a little more subtle than how you describe it.
The gunfight between Hitch and Bragg was legal...by Old West rules. Hitch had turned in his badge making him a "common man" again an no longer bound by the behavior required by a lawman (I think Bragg even makes a comment to this effect to which Hitch responds that he is no longer a deputy). Bragg could have ducked out the back and ran away again (like he did in the earlier fight) but, as a respected businessman in town now, his pride could not accept the humiliation.
Injuring another man's pride to the point where he will fight a duel with you is not grounds for murder, so Cole would not even have grounds for an arrest. It was a fair fight and half the town saw it including most of the town leaders.
On the other hand...Cole had just gunned down a rich and influential businessman who had contacts with the president of the United States AND probably still had connections with his old gang. Just like with the young boy who had witnessed against Bragg at the trial, getting the hell out of town was not only vital to his own health but, in hanging around, Cole was sure to get involved as well which was the opposite of what the fight was all about in the first place.
Because Hitch had killed Bragg as a means to help Cole have a second chance with both his law career and with Allison, sticking around just really wasn't an option.
As for Katie (the Russian girl)...I really wouldn't call their relationship "the marrying kind". The woman was a prostitute and Hitch probably paid her for every hour they spent together. She did offer Hitch some really good advice, but I'm not really convinced that they held any real feelings for each other, except maybe as business friends (she didn't seem all that broken up about his leaving for example).
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