Erectile Dysfunction

My husband takes cymbalta and it is causing the same issue as his other antidepressant he switched from.  we can only have sex when he gets his 4 pills from the doc (viagra). he is 36 years old. he rarely ejaculates during vaginal sex only anal.  he doesnt wanna get off the meds due to really bad bipolar.  he also takes ambilfy. any antidepressants that dont cause this issue?  sex is such a challenge he cant get hard or stay hard longer than 30 seconds. i am supportive but deep down i feel cheated and that i am too young to deal with this the rest of my life. Sometimes i hope he screws up so i can file for divorce with a legitimate reason. i like sex what do i do? his four pills are monthly prescription