Pls Help! I have poor erection with my GF, but a normal with other girls

A young man has discussed his abysmal s*x life following his 4-year relationship with his partner.

He has been suffering issues of weak erection during s*x with his long-term girlfriend but on the other hand, he is always very strong and active whenever he sleeps with another lady.

His relationship is almost crashing and he has written to a relationship blogger, Joro Olumofin for assistance.