Yeah I agree it's most likely a tolerance thing and not that you're bored (do you ever truly get "bored" of sex? More likely it's the same routine over and over that makes it less exciting).
It took a year and a half of daily dilaudid use before it basically stopped getting me high. Now, the best feeling I have to look forward to is taking the meds when I'm having moderate withdrawals - the transformation is amazing, going from feeling like total shit to "normal" in 60 seconds.
But that's the best I can do these days. Despite popular belief, for some reason taking more does NOT work for me, so even on special occasions, I can't just double (or even triple) my dose and get high again - it just stopped working.
On the other hand, I recently was given a fentanyl patch and tried that for the first time (plugged it) and THAT gave me my beloved opiate high. I don't know why it worked, opiates is opiates is opiates, but for some reason it did.
Sadly, I have no access to fent - I'm "stuck" with dilaudid (I know, poor me), but the whole point is maybe even just another opiate would bring back the magic for you.