http://time.com/3596014/attraction-sex-birth-control/

In the mating game, there is behavioral courtship and then there is chemical attraction/disgust. Red Pill does a very job of teaching guys how to behave by maintaining frame and practicing game. What I have never seen outlined on Red Pill though, is how pheromonal signals can help you get laid. . . or spell disaster. I'm going to outline in some detail how this process works, but you can skip the technical stuff if you're not into it. The main idea is that organisms can essentially sniff out which mates are not only genetically fit, but which ones are a good individual match genetically - that is, which will produce the strongest offspring with YOU. The same way sugar smells sweet and shit smells disgusting because these signals enhance biological fitness by promoting ingestion or avoidance, respectively, the scent of a potential mate is either relatively pleasing or disgusting to a human being (particularly women, who have more to lose by making a bad choice) because it helps promote biological fitness in reproduction.

So if it is largely just random chance that determines whether you and a woman match up, why does this matter?

The bottom line that needs do be driven home is that hormonal birth control distorts a woman's ability to correctly identify which men are a good match with her genetically, on an immunological level. Therefore, if a girl is super attracted to you when she is on the Pill, it may very well be a false signal she is responding to. When she settles into an LTR or marriage and goes off the Pill, her dissatisfaction and/or inclination to cheat may have nothing to do with your behavior and everything to do with the fact that the other guy ignites a biochemical feedback loop in her brain promoting attraction. You, on the other hand, now provide signals promoting disgust because her receptors aren't being distorted anymore by the Pill.

How does this work? The human immune system has been categorized into what are known as major histocompatibility complexes (MHC). When you produce offspring with another person, it is best if they have as much differentiation from you as possible because this secures immunologically diverse offspring. If some fatal disease comes into town it may therefore be prone to only kill your wife and half your children, as opposed to every single one of you in the case that your immune systems are the same. Different immune systems means you are better at fighting off different diseases, and therefore greater chance at least some offspring survive.

The evidence that women can detect histocompatibility and that it is highly influential in there attention to certain men is strong. The evidence that there is a reverse effect when they are on the birth control Pill is also strong. Nightclub studies have been done all over the world to demonstrate this. Universities too have shown the effect in various surveys and laboratory experiments.

I'm not going to cite all the primary sources ad nauseum (you can do a simple google search) except to provide an article which is somewhat comprehensive in outlining the topic. Anyone with half a brain can see this how this can have major effects for any LTR or marriage. It's necessary information to digest if you are considering an LTR/marriage and want it to last.

Tl; dr; Birth control fucks up a woman's ability to choose a quality mate. Proceed with caution. Your behavior may not be at fault for her loss of desire if she has gone off the Pill.