Why would my friend say that...I'm quite confused...?

I was with a married guy for a while but never knew he was married...when i found out i put an end to it right there and then! I am not a ! after i broke up I called my best friend and told her what happened...She said some stuff that reallly bothers me. stuff like "why did you end it" after i told her that he was MARRIED, "if you really like I'm i don't see the problem"...This happened a while back, less than a year, but i was focusing on dealing with betrayal then with my friend...I just now realized what she had said to me... If she's my best friend and wanted the best for me what would she say that?? And she's married! That's the part i don't get!!