Is severe fear of insects and other non-human living creatures, which affects marital life and causes embarrassment and awkward situations, considered a form of fearing other than Allah, and is it a sin that requires repentance, or is it a natural matter?

Fear of harmful creatures is natural, but if it reaches the level you described, it is an illness that requires psychological specialists. Ruqyah (Islamic exorcism/healing) is recommended, as is persistence in acts of obedience and remembrances (dhikr), and avoiding sins.