To expand, my original question was whether it was possible to be with the same person sexually for a lifetime and not get bored. I also mentioned that I was interested in an open relationship, but my fiance was not. Here are some of the other replies I received:
"U R NOT ready for marriage -- U still have lust issues. An "open" marriage" is for immature people who are easily bored out of immaturity."
"open relationships are for people who are over-sexed (beyond the normal high sex drive of healthy people). Open relationship + happily married long-term = extremely rare."
"Entering a marriage thinking its gonna be boring & you should see other people means youre not ready to commit to your fiance"
"People have stayed in jobs their whole life despite the boredom. If you told your boss that you want an open work relationship how do you think he/she would take that?"
"Your fiance needs to get out of this relationship ASAP."
"Thinking that sex with the same person for the rest of your life is boring is immature."
"If you all think fcking other people is fine that's your choice, but its pretty sad that you think this is normal or acceptable"
"It is sad you are already interested in having an 'open sexual relationship' when you are not even married yet."
"If you are wanting an open relationship, and aren't even married yet, that means you aren't ready for marriage. Marriage is about monogamy."