Röhm and Hitler were friends for a while. Röhm was one of the very few people who was on a first name basis with Hitler, using the familiar 'Du' rather than the formal 'Sie'. But at the same time they had diametrically different ideas about the role of the Party, SA etc.
Hitler regarded the SA as an auxiliary formation that served the Party. It was not supposed to be an army-in-waiting or a paramilitary force that could match the military. That was the lesson he learned after his failed putsch in 1923. The SA was supposed to look good marching, protect Party rallies and beat Communists in the streets. But that was it. Röhm, by contrast, wanted it to evolve into a National Socialist army. And he saw the soldier as more important than the political leader and disliked the 'legal path to power' that Hitler pursued after being released from jail. Far as I know, there's no proper scientific biography about Röhm yet, though Longerich has written a good book about the SA as an organisation. Some secondary literature works claim he favoured rapprochement with France, but I haven't researched the matter enough to assess how accurate that is, so take it with a grain of salt.
Much has been made about Röhm taking the Socialist part of National Socialism more seriously than Hitler, but what he wrote and said about the 'Second Revolution' was vague. However, he definitely disliked Hitler's compromises with the old elites in the bureaucracy, army and big business. It is pertinent to note that many SA members felt that they had not been 'given their due' after the seizure of power. Sure, they got the chance to settle 'old scores' by abusing and murdering Communists, Social Democrats and so on. Several SA leaders became police chiefs. But their camps were soon closed, they lost influence in the police and overall the true winners were the Part bureaucracy, not them (there was bad blood between the SA and the Political Organisation of the Party). They wanted to be a 'revolutionary army' (though what that revolution would actually entail on a practical level beyond violence and getting privileges that had been denied them remained nebulous), but their own Führer told them that the revolution was over.
Hitler and his cronies claimed that they acted in 'self-defence' when they purged the SA, but there is no evidence that Röhm was planning a coup. Hell, the SA was on holiday. He and his men were caught by surprise when Hitler and his guards showed up at Bad Wiessee to arrest them. Now from a pure numbers perspective, the SA was bigger than the Reichswehr (and the SS). But many of its members were ruffians, not actual soldiers by that time. Exploring a scenario where the SA (or say the Strasser wing) is ascendant could be interesting, but many variables would have to change.