Sometimes good relationships end early because of bad sex:

To overcome this challenge, you must first identify the cause of the absence or lack of quality in sex. Sometimes the issue is low sex drive which can be hormonal/biological or due to stress or emotional strains. Unlike popular belief, people who cheat sometimes, don’t always show a decrease in libido, because the source of the infidelity may be emotional or intellectual. Other times, it is because a lack of communication. If you feel shy to discuss sexual issues with your partner, you may have to reevaluate your openness and honesty with your partner, you shouldn’t ever feel ashamed to express what you like, don’t like, and fantasize about. Being open in communication will not only bring you closer, and improve the sex. Sex is a learned and socialized thing and it is not set in stone, if your partner is bad you can always fix it.