I have endometriosis, must I have a hysterectomy?

No. Many women with endometriosis do have a hysterectomy at some point but that is a very individual decision. Most women do not need that. But surgical intervention can be needed for pain, for cysts, and for scar tissue at some point.
No. Non-surgical treatments for endometriosis include 1) gnrh agonists, like lupron, (leuprolide) that cause a menopausal-like state to shrink the endometriosis, 2) oral contraceptives which may treat the symptoms and prevent progression though they will not cure endometriosis, 3) laparoscopic excision of all active endometriosis with lysis of adhesions, 4) pregnancy, or 5) menopause. Talk to your doctor.