A.T. Robertson Commentary Luke 8:38

"But the man from whom the demons were gone out prayed him that he might be with him: but he sent him away, saying," — Luke 8:38 (ASV)

From whom the devils (demons) were gone out (αφ' ου εξεληλυθε τα δαιμονια). Past perfect active of εξερχομα, state of completion in the past.

Prayed him (εδεειτο αυτου). Imperfect middle, kept on begging.