How much can i lend to my best friend???

This is what I believe: if a friend is in need of money, give it willingly if you can afford to and don't expect repayment. If he pays you back eventually then consider it a bonus. Expecting friends and family to repay money just leads to hard feelings. If you can't afford to help him out, be honest and tell him so. I don't know your faith, but the Holy Bible tells us to help out those in need and we will receive our reward in Heaven.