He said 'It's not a full-on relationship but it's been going on for a while', what does he means?

His girlfriend broke up with him a few years ago but when I asked him his status, he said 'It's not a full-on relationship but it's been going on for a while', what does it mean? should I leave him alone or pursue a relationship with him?
He said 'It's not a full-on relationship but it's been going on for a while', what does he means?
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