should i write him?

my real dad walked out of my life before i was old enough to remember him. hes in jail now and wrote me a letter, 18 years later asking me to forgive him and write him back. all along my mom married a great guy who ive called dad since he adopted me at age 5. i love him and i feel like if i write my real dad then it would be disrespectful to the man who raised me. what should i do..?