Should i give this guy a third chance?

hey,listen everyone here. i have this one person who is trying to be my friend again. thing is i believe in 2nd chances and i already gave this dude his. he broke my sister's heart twice, and betrayed my trust twice, he says he is sorry. i want to believe him but my gut says no. i have stabbed in the back 2 many times b4, wat do u guys think?