I generally feel it's best to be responsible for yourself and only yourself, and leave your partners free to make their own choices. Anything short of that is unlikely to be sustainable.
Is it reasonable to want a pet who will greet you at the door and sit on your lap when you watch tv? Sure. Is it reasonable to get a goldfish and expect it to meet you at the door and sit on your lap? No.
There's nothing unreasonable about wanting your partner all to yourself. It's the cornerstone of monogamy. But dating a poly person who's dating someone else, and expecting them to behave in a way that's contradictory to their nature? Probably not gonna work out.
For the record, a "boundary" is not the same as a "rule" or "agreement."
Boundaries are limits you impose on
yourself; e.g. I will not stay in any relationship where my partner is having sex with other people.
Rules are limits you impose on
other people, and are really only valid when you're in a position of authority over them (e.g. parent/child, employer/employee).
Agreements are where two people
consent to limits (or expectations) on their behaviour. Might seem pedantic, but it's important to think of them as different things.
You're always allowed to have any boundaries you want in a relationship: boundaries are all about you and what behaviours you'll tolerate from other people.
You're never allowed to make rules in a relationship: rules are always about authority. Agreements can be made by any group of people, but those agreements should align with actual intentions and desires. Agreeing to something you prefer not to do, or worse agreeing to something knowing you don't intend to follow it, is never in the recipe for health and happiness.
There is a difference between coming to compromise like taking turns and compromising one's preferences/values.
i.e. the difference between compromise and sacrifice. Compromise is where both parties are more-or-less comfortable with the agreement. The best compromise is when both people feel like they "won." But no one should feel like they "lost" in a compromise, otherwise it's a sacrifice. Relationships built on sacrifice are doomed.
Assuming Harold and Joann actually want to have sex, there's really no way to "compromise" -- either they have sex, or they don't. If they do, then Jane is sacrificing her value of sexual monogamy. If they don't, then Joann and Harold are sacrificing their value of sexual expression.
If everyone involved is sexual (i.e. not asexual), then I believe having a limit of no sex ever for one 'arm' of the V is not ethical or practical.
Education opportunity!
Asexual means lack of sexual attraction. It's an orientation, specifically that the group of people to whom you tend to feel sexually attracted is "no one." It is not the same as having no sexual desire. An asexual person can still want and enjoy sexual relationships with their romantic partners. I think of it this way: I never see a hottie from across the street and think "I'd spread my legs for them" but I do feel sexual desire, generally responsive, with certain people; and I experience arousal at all kinds of awkward times (like watching the animal channel...)