OP just asked how people tell their SO they want to have sex, not how to convince their unwilling partner to have sex. Plenty of people wind up in phases of their relationship where they aren’t having sex as often as they would like, which can be the result of many different factors outside of the relationship. Particularly if they’ve been together for a very long time. It doesn’t mean anything is wrong with the relationship.
OP just asked how people tell their SO they want to have sex, not how to convince their unwilling partner to have sex. Plenty of people wind up in phases of their relationship where they aren’t having sex as often as they would like, which can be the result of many different factors outside of the relationship. Particularly if they’ve been together for a very long time. It doesn’t mean anything is wrong with the relationship.