This is Metamorphosis Odyssey Book Two. Metamorphosis Book One was serialized in Epic Illustrated (Marvel, 1980 Series). The Metamorphosis Odyssey continues in Marvel Graphic Novel (Marvel, 1982 Series) #3 Dreadstar
Syzygy Darklock makes pacts with dark forces in order to gain mystical powers. He is nearly killed and ends up sacrificing his one true love, Sister Marian, to demons that he might achieve his destiny.