Choosing Satan as a patron instead of Allah is the root cause of committing Shirk which God does not forgive!

Verses 116-121  of Chapter 4

Lo! Allah pardoneth not that partners should be ascribed unto Him. He pardoneth all save that to whom He will. Whoso ascribeth partners unto Allah hath wandered far astray. They invoke in His stead only females; they pray to none else than Satan, a rebel.Whom Allah cursed, and he said: Surely I will take of Thy bondmen an appointed portion. And surely I will lead them astray, and surely I will arouse desires in them, and surely I will command them and they will cut the cattle' ears, and surely I will command them and they will change Allah's creation. Whoso chooseth Satan for a patron instead of Allah is verily a loser and his loss is manifest.He promiseth them and stirreth up desires in them, and Satan promiseth them only to beguile.For such, their habitation will be hell, and they will find no refuge therefrom.