I'm Seeing My Best Friend's Ex Boyfriend And I Don't Know If I Should Tell Her Or Not?

You should not be afraid of this and go ahead and tell you best friend about this, what if she still have feelings left for him and seeing him with you breaks her badly, what if she knows something bad or maybe good bout' that person that you should know before you go ahead and continue with him.... You should tell her also because this might clear a chance of a miss understanding that she might have for you as you are seeing her ex..... Telling her will only be a good thing but nothing bad.....

Best to be upfront with your friend  as there may be bad feelings if you don't.  I have seen people argue over others as well have been hurt myself. The worst is finding it out from someone else

That could be a really touchy subject.... It depends on how long ago did they separate.... If recently better not say anything she may think that you are the cause of the break up... If a long time like a year or so then mention that you saw him around and you think he is good looking and would she be upset or mad at you if you tried going out with him... How much do you value your friendship...

The problem is, sooner or later she is going to find out.  Whether you tell her or it gets back to her through the grapevine, she isn't going to be happy with you.  That is just how women are....we don't want the ex..(or does she?) but we don't want him to have anyone else either ..and certainly NOT our best friend!!!  

Ask yourself:  Would you rather find out through another person that your best friend was now with your ex, or would you want to hear that from your friend directly?  

Either way, your friendship is going to be changed.

You should tell her....and u shouldn't even see the guys...there's probably a reason he's an ex
And its just rong to even think of even going out with him..considering its ur best friends ex.