If they are STD free and you know this to be a matter of fact, you have no worries, but I would certainly NOT advise that you contiune this habit of dual sex partners unprotected.
The reason for this is because you are not aware of their sexual activies aside from you, so keep your self protected for your own sake.
Best wishes
Clean is not the correct term. STD free is. If neither is with anyone else and don't have a STD then no.