Taking deca durabolin. Will this greatly increase my acne?

Maybe. I've supervised bodybuilders on steroids; many if not most regret it afterwards, but it's your decision. Any anabolic steroid's effect on acne is unpredictable. Fortunately, it's usually easy enough to control acne with topical antibiotics (i prefer clindamycin), systemic antibiotics (i took tetracycline for decades) or for hard cases, a dermatologist-prescribed Accutane rx. Good lcuk.