Unisexual

Unisexual, also known as onesexual, unianthrosexual or unosexual refers to someone who feels attraction towards one person and one person only for advanced periods of time or perhaps one’s whole lifetime. This is a more specific form of greyasexual, in which one only experiences sexual attraction a very small amount of times in their life. Once one is attracted to someone they will not experience attraction to anyone else. One will be attracted to this one person regardless of the their own or the other person's changing gender, sexuality, or appearance. One will be attracted to this one person for a long period of time and feels as though they will not experience attraction to anyone else for the foreseeable future.

A similar term is soloamare.

History
Unisexual was coined on or before July 8, 2016 by the now deactivated Tumblr blog pride-flags-for-us.

Unianthrosexual was coined by an anonymous wiki user on 9/10/20 as an alternative to the unisexual label. This was done to prevent confusion, as unisexuality also refers to sexual and/or gender neutrality. It literally means "one-person-sexual."