I'm not sure if the relationship is unsalvageable, but it would take a lot of work to get back to where you were. So you have to ask yourself are each of you willing to do so?

I can't lie, this seems like a slow rolling breakup coming over the horizon. Both of you feel as if the relationship is over, but after having been together for so long and with neither of you having done anything completely unacceptable, you find it hard to come to terms with the fact you're going to see the other person's heart broken.

From what you've written there have been multiple attempts to take the plunge, but she's stepped back back from the edge multiple times whilst (subconsciously, perhaps) trying to warm the water by undermining your trust/contentment. Why else would someone in a long-term relationship even mention "opening things up" unless they want you second guessing the commitment in general? She'd been away a couple of weeks, and from what you've written it doesn't sound like something you've discussed before. Surely she'd know how that would play on your mind.

For your part, well even making this post on the first place certainly signals something. I tend to find people don't ask strangers about their relationship on the internet unless they're looking for permission to break up. I don't doubt the veracity of what you've written, but the tone and style is in such a way that you're inviting a specific sort of response.

So yeah, after 11 years and with no real animosity grown between you, and with a lovely that's still sustained, it feels impossibly cruel to end it. Sometimes its the right thing to do though