I have had my braces off for 5 years. i had a gap between my two upper teeth. after treatment a permanent retainer was put in place. lately i have noticed a small gap forming back but the retainer is still there what to do? will the gap close back?

See your orthodontist for advice. The diastema which is forming will not close by itself.

Gap means teeth are moving. Perhaps teeth are moving (bone loss). because of normal bone response to change in overall occlusion, or wire is partially disconnected, or you have not been flossing and may have bone loss. See both your Orthodontist and your Dentist. This will only progress with time.