Is it normal that i have feelings for my bestfriends ex?

Recently my bestfriend cheated on her "love of her life" But yet she cheated on her ex with his Bestfriend. I've told her that it's wrong and that she can't just do that without telling her ex what she did. I have been there for my bestfriends ex because she hurt him, and i've been hanging out with him. At first it was just innocent friends hanging, out cheering him up. but, now i've gained sort of feelings for him, and i am confused like crazy, and i want to know if this is normal to have feelings for my bestfriends ex?