Abram left Haran because God told him to do so.
Genesis 12:1Now the LORD had said unto Abram, Get thee out of thy country, and from thy kindred, and from thy father's house, unto a land that I will shew thee:
Note that the calling of God to Abram came BEFORE he dwelt in Haran. Genesis 12:1 says that the LORD had said unto Abram...
Act 7:2,3And he said, Men, brethren, and fathers, hearken; The God of glory appeared unto our father Abraham, when he was in Mesopotamia, before he dwelt in Haran, 3 And said unto him, Get thee out of thy country, and from thy kindred, and come into the land which I shall shew thee.
I hope you have found this helpful.
May God bless you,