He made a deal but the rebel alliance kept on moving the goal posts. Anyway, what allies could he have reached out to that would have enabled the UK to have left on the 31st?
How about Labour, who you have helpfully pointed out multiple times that they are not exactly against Brexit? How about the rebel Tories, of which ignoring their concerns only resulted in them splitting from the party? Dealing with both parties would require a certain amount of compromise that stands a good chance of leaving no one particularly pleased, but even that is better than the alternative of this stupid multi-years long deadlock.
Brexit may have been a lot about principles, but it's high time that reality set in. The reality is that in order to pass Brexit, it must pass legislation, and in order to do that you must have the votes to do so. Pruning your ranks of 'traitors' is counter productive to this goal. The need for votes necessitates two strategies. One is to hope that, eventually, the people vote in enough of one side or another to finally reach a decision on this matter. A risky gamble and one I don't see working any time soon. The other is to compromise enough with the people you can reach some sort of common ground with in order to get the necessary votes to pass. A bitter pill to swallow, but a much more assured path forward than hoping the populace 'votes correctly this time'. So really, the only question that needs to be asked of the public is "Are your feelings on Brexit, whatever they may be, so important that you would rather potentially drag this out for years, if not longer, rather than seeking a compromise resolution now?"