The thing about exes is that they know all your flaws and they will use them against you. So, if he sees that you forgave him last time he will cheat on you again or will hurt you in any way, thinking that you will forgive him. Thats why you should never give him a second chance.
Are second chances okay?
If your partner has learned from whatever he or she did to you, and now knows how to make things right, its OK to consider a second chance. If you feel like he or she doesnt understand the repercussions of his or her actions, then nothing has been learned at all — and sadly, nothing will change.
Why do guys ask for second chances?
He deserves a second chance if he shows you that hes changed, that hes ready for a serious relationship with you and is done with the games, done with the back and forth, done with playing the field. If he makes it clear that hes worked on himself and is ready to accept your love and give love in return.