If orgasm triggers bonding and feelings of love, why don't people continue to stay in love? I am a bit confused by the effects of orgasm in bonding; everything I seem to read seems to be a bit careless with the truth and does not mention why people fall out of love or why people who are in relationships cheat, etc. Could anyone please elaborate?
Surely, orgasms do release drain out dopamine but you're forgetting another important factor in dopamine release, which is novelty.

Ever heard that couples get bored of sex after an year or two? It's because they find it routine and boring. Cheating (an e.g) gives you the thrill of novelty.

The same activities which we find thrilling / rewarding will not remain that way. It has something to do with the sensitivity of dopamine receptors. Take novelty seekers (e.g) they tend to find novel activities thrilling.

The worst scenario occurs, when a person no longer finds any activity interesting. That is nothing but Anhedonia.



EDIT: I'm sorry, but I just realized that staying in love is a bit different from enjoying orgasms after reading this. A relationship is far more complicated than just producing enough dopamine.

Release of enough endorphins, helps you stay happy, if you're happy you're likely to not hate other people around you, if you do not hate them, you're likely to like them by releasing enough oxytocin (physical touch etc.). Apart from that, a sense of responsibility and well being comes into picture when you're serotonin levels are moderate.

Definitely low dopamine levels is a cause, but not the only cause of cheating etc. Any imbalance of neurochemicals causes not only relationships fall, but also other unhealthy / anti social behavior.