J.A.
First- Congrats on 26 years! Second- I'm sorry you've been through so much! I know first hand about the money woes and infertility. Both of those can have a HUGE toll on you marriage.
As for the "how long is too long" question: according to a family theripst that was recently speaking to a ladies group at my church, medically speaking, a man needs to release at least every 3 days. I know! THREE DAYS! What in the WORLD do they need it that much for??? But- according to her, that is the "magic number" to insure his long term health.
Just as an FYI- I am sure you already know this, but Anti-depressants can have a negative effect on your (and his) libido. I was on Lexapro for a VERY short time (pulled off to countinue infertility treatment) and had a possative libido inpact. I am not sure if it is "good for most people's libido" but it was for mine. (My hubby asked if I could go back on it after we have our baby in November, even though I don't think I will need it then! LOL)
Anyhow, talk to the Dr about whether a different AD might have a better "sexual side effect" for each of you. If all else fail- get creative in the bedroom. Force yourself to THINK you want it, and sometimes you actually really do by the end of the day. Wear a sexy bra and underwear or a corset, and by the end of the day, you may be excitted to get it "going" that night.