pistol69

how is it dangerous?

I would say it largely depends on the value they each put on sex and their reason for doing it. If they each see it as purely recreational fun and are doing it for the sheer pleasure then sure. However if one or both are doing it to fill a void of intimacy or a craving for validation then I would say it will eventually lead to feelings that could be problematic. The reality is that feelings sometimes show up where they really aren't supposed to.