Some people are truly monogamous and I respect them. Some people are truly not monogamous, and open relationships are not for everyone.
The concept of marriage does NOT belong to any one single culture or religion, and the concept has been around much longer than organized Christianity. So, marriage does NOT equal one sex partner for the rest of your life; that is a Christian concept, among others.
Sex and love are NOT the same thing, one does NOT equal the other, so stop treating them like they are! Wanting sex from someone doesn't mean that you love them, so why would wanting sex from someone mean that you don't love someone else?
There are a few monogamous people out there who can handle being in a relationship with someone who is not monogamous. It's called loving someone enough to accept them for who they are, and letting them be it. They're not being "cheated on". They know what's up, and they are OK with it. That's their business, and it's not your place to tell them how to be happy.
Marriage is not a business, and neither sex is obligated to perform in any specific way. That is a matter of personal preference, so stop assuming that others believe in, or follow the same ideals. No man is obligated to completely pay the way for his woman, no woman is obligated to be the "house bitch" and wait on her man hand and foot. If that's what you like and how you like it, then I respect your right to your preference. Marriage is a partnership, and requires an even amount of work from both parties, in whatever form you can offer.
No relationship of any kind, closed or open, can work without trust.
Open relationships of any kind, go both ways. If they can go out and see other people, you can too. But BOTH of you have to be on board and agree that it's what BOTH of you want.
There are many financial benefits to marriage. Discounts on insurance is the biggest. There are legal and social benefits to marriage. Like when I tried to visit my ex husband in the hospital. There was a strict "family only" policy. I was allowed in, still having the same last name, but his girlfriend was not. These benefits are the perks awarded to whomever makes the best domestic partner, or gifts to whomever we love.
Who you have sex with holds no bearing on who you love or how much you love them. Who you have sex with has no effect on your ability to be a good roommate, or a decent person.
Marriage has nothing to do with love or sex, it has everything to do with security. But people usually feel most safe with those whom they love the most, thus the concepts have become intertwined.
Marriage does not change you, and should not change the mechanics of your relationship. Think about it! You're getting married to them because you love the relationship you already have with them.
Marriage doesn't magically make a player faithful, nor does it provide any guarantee of loyalty or protection from cheating. In fact, it is impossible to "cheat" in the first place unless you are actually committed to that person exclusively, so one could argue that only those in relationships cheat.
If you really don't trust them, you shouldn't even be dating in the first place, but get a prenup, if it makes you feel better.
If they were already open before, don't expect them to magically change and become monogamous in marriage. Being monogamous, or not, is no different than being gay. It's just part of who you are. Acting on it, is a choice. Many non-monogamous people go though "dry-spells" where they're not interested in sex, just like any other normal person. Those that engage in relationships will go through periods where they only want their partner, and won't be interested in others outside the relationship. Try to keep this in mind if you're considering any kind of relationship with a non-monogamous person.
It's not "cheating" if you both know it's happening, agree to it, and give consent. Cheating, by definition, is when you engage in ANY sex act without the knowledge and consent of your partner.
And finally, to those that have made comments comparing it to marrying a prostitute or a stripper: I'm not getting paid. Do you assume the prostitute would keep whoring around if you could afford to care for them? I don't know of many strippers or prostitutes who do it because they like it. The two concepts are not connected.
If you want to discuss this politely, just message me. I'm happy to answer questions as long as there is mutual respect.