Relationships fail because attraction falls. Since we're mainly guys here, I'll focus on our end, and her attraction to us.
Game in long-term relationships is striking a balance between being sexually attractive and emotionally available. Being too "alpha" tends to emotionally alienate women. Being too emotionally available tends to turn them off sexually.
Most of the dating advice herein is focused on short-term pickup, hence, the preference here is heavily skewed to being "alpha" and "being dominant" and "holding frame" and "never ever doing x with a girl" and "never ever saying y to a girl" etc.
Little advice here deals with the inevitable, inescapable fact that women leave alphas for betas all the time when the beta offers her emotional validation and closeness that is so frowned-upon in red pill "alpha male" circles.
Giving your LTR the highest chance of success will require you to be both -- to satisfy the duality of female mating strategy. The best way to do that, the ideal balance, depends on the individual woman you are dating. Generally speaking, it's maintaining a masculine leadership role in the relationship, while also being emotionally nurturing.