Sexual side effects with SSRIs have a strong correlation with age, that is, the older you are, the more you are likely to experience these side effects. I was on zoloft for 7 years, 150mg max. One thing that I noticed is that zoloft made me content with my lifestyle and relationships. When something sexual presents itself, it has the ability to alter your mental state/stability, so when your on this medication and one of these situations arises you may be physically affected (not being able to orgasm), to try and prevent a change in your mood.

My advice would be to choose your sexual partners carefully, choose someone you feel comfortable with.