Nothing wrong with following the heart some of the time
If your brain agrees with your heart go for it.

But this girl is playing you and your brain knows it.

Come on grow some balls!

Tell her straight up how you feel. If she gives you any bs and still wants to date this dude, walk away and never look back.

If she wanted to be with you she would not be dating this dude. Period!

Life is to short to be strung along by a girl. There are thousands of beautiful girls out there. Go get one.