Sexological therapy can be relevant, both on individual or couple’s terms.

Maybe you never enjoyed sex fully, maybe you have problems with erection, orgasm-difficulties, or troubles only when being with a partner. There can be physical pain attached to sexual practice, that makes it almost impossible being together with another person.
In that case, it is important to have a doctors examination, to make sure nothing physical is the matter.
You may have considerations about your sexual orientation, which might be hard to talk to friends about. Or maybe you’re dissatisfied with yourself, having too many casual sexual relationships.

As for couples, you might have had a passionate sexual life in years before, but now it has become boring, complicated or non-existing.
Or the classic version: one partner prefers sex more often than the other. In that way even an innocent kiss, can turn into a ’threat’.