They are friends with benefits, not a couple.
friend with benefits
idiomA friend with whom one has a casual sexual relationship.
Origin
first recorded 20th c. disputed originPossibly first used by Alanis Morissette for her 1995 song “Head over Feet”, although in the original context it seems to refer to a committed rather than a casual relationship.
She decided to keep things casual and became friends with benefits with her neighbor.
While they enjoyed the intimacy of being friends with benefits, they both knew the arrangement could not last forever.
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all-weather friend
One who is friendly, helpful, or available at all times regardless of the circumstances.
- 02
asking for a friend
Indicates that a question is embarrassing by pretending to be posing the question on behalf of another person.
- 03
fair-weather friend
One who is friendly, helpful, or available only when it is advantageous or convenient to be so.
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feathered friend
A bird.
- 05
fine-feathered friend
A well-dressed person.
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friend of Bill W.
A recovering alcoholic, especially one who is a member of the organization Alcoholics Anonymous.
- 07
friendship with benefits
A platonic friendship where the partners engage in sexual activities, but do not consider themselves a couple.