It sounds like you want to be able to handle it
but the situation you are creating is probably going to end up in a lot hurt. Like others have said, you cannot stop yourself from falling in love. But Love doesn't have to be restricted to the definition of Love like that of a primary partner, just because she will never be anything more than friends, and the relationship includes sex, is no reason you cannot love her unless you decide it can only be that way. Some people even feel it has to be that way and it's just who they are.
If you are going to be as close with her as you are telling us you have been, it will be extremely hard to put restrictions on her about not being able to share things with you. It is all but impossible to have a healthy friendship with a person going about it the way you are. Talking as much as you do, and her not being able to mention any plans until after the fact won't work unless you are able to employ some super serious denial. It is like setting your clock fifteen minutes fast, and then expecting yourself to "forget" its not fast. It will help you to not be late, but I don't know anybody who can honestly believe their fast clock isn't fast when they see clock that isn't.
that analogy might not make sense until I add that the situation would be as if every time you failed to "forget" your watch was fast (which is every time you had to be somewhere at a specific time) you get all butt hurt about it.
Getting butt hurt was kind of harsh, I don't mean to down play your feelings. However you are going to have to find a way to get over the fact that you are not her boyfriend, because otherwise if you don't change anything you are doing it will damage her relationships or your ability to be emotionally happy and stable. Continuing on without changing, will cause damage. So even if you are mature enough for the damage to not affect her other relationships, the damage will all fall on you emotionally. If you let this happen, you are not treating yourself as well as you need to be.
If you are honestly are as close friends as your story sounds, you won't be able to remain in denial about it being as casual as you or her are labeling it. This is a tough situation because you need to keep in mind she has spouse and that is a relationship you need to be respectful of. But if he and she are willing to let you be as close as you are, and she is as sexually active as you are making her sound, one way to get over your jealousy issues that I would recommend is to witness her having sex with another man. It goes without saying that she and the other man would have to be OK with that, but it has "cured" people of their jealousy issues, however it can open up a whole nuther can of issues, as it can become a fairly kink, that now takes three people to all be onboard and desire the same thing.
But you may get lucky, if she agrees to it once and after she knows she doesn't like being watched, hopefully witnessing that which you had trouble accepting will be enough for you to accept the sex acts with others so that you can remain healthy friends with each other.
Because if you continue to have the trouble to the extent you describe in this thread, something has to give and it eventually will. Unfortunately not recognizing this will may wreck your friendship beyond being repaired and it's not pleasant, not matter how much anybody wants it to be.
There are no absolute laws in friendships like this and it would be great if you could defy the likely outcomes of what countless others have experienced, which pretty much doesn't stray far from casual relationships needed to be kept casual. And closer relationships needing to remain close which means open, honest, and without rules that enforce rituals such as living in denial.
Hope all can be maintained the way you desire it to be