Hi lamf10 & welcome.
All you need to do is ignore the people who are making these wild assumptions and even wilder accusations.
You know that your relationship with this friend is innocent friendship.
I assume that she knows it, too, and that both partners know all about it.
Provided everything is truthful & in the open, between the four parties involved ~ the ones who count ~ and that you all know the truth, and trust each other, then it is nobody's business but yours.
There is no need for this to be a mess, if you simply ignore those people who are not involved.
I suppose, if they are parents, perhaps, then you might be understandably upset. Are they?
If so, just try to explain to them that you are not a cheat and that you would appreciate their support in this.
Good luck!