Oh, he is just my part-time boyfriend.
It can be a positive relationship where people who don't want to be alone, but aren't wanting or able to be in a full-time/exclusive relationship, can have a friend to do activities with. It can be sex based, or include other activities and sharing. It can be more than just a friends with benefits relationship as well.
It can also be a negative relationship, where one is cheating or leading on a partner and avoiding being exclusive. It can be just about sex, it depends on the individuals involved.
obviously not he's a part time boyfriend he can't be bothered.