First, I'll admit to not reading every post in the thread.
My first marriage: We were young, I was active duty in the Air Force, far away from anyone I knew and anything that made much sense (stationed in California at the time). My first wife and I had a few common interests, but admittedly, my interests were constantly changing. I latched on to the shared interests we had, and convinced myself they were genuine despite the fact they were already flagging. I tried the 'fake it til you make it' approach, but it didn't work. My interests and beliefs changed, simple as that. I changed, she didn't. I was a suburbanite kid from Kentucky, she was an emancipated teen who grew up in San Francisco, we were worlds apart. Also, I'm naturally selfish. I know this. For a very long time, I had a level of disposable income where I could afford the toys and accoutrements of my interests. I accumulated a lot of junk, and again, my interests changed from month to month. Anyway, over time, she grew more liberal, I grew more conservative. We tried counseling, but neither one of us wanted to accept any fault, knowing that we each had problems, but didn't want to face them in ourselves. Counseling doesn't work unless you're both willing to be honest with yourselves from the first second.
My current wife and I have a few more similarities and common interests. For the most part, my interests have finally settled into a more predicable pattern, which now includes guns. I do still have some of the same selfish behaviors, and my impulsive purchases haven't been completely curbed. Mostly, but still not totally. She grew up around guns, and enjoys shooting, just not as much as I do. She doesn't like my SKS, but handled my buddies AR-15 yesterday, and she liked it. So naturally, my thoughts drifted to a purchase of an AR-15. She liked it, so what would be the problem?
The problem is me. She liked the AR, but there are a lot of things she likes a lot more than the AR, and the purchase of the AR would honestly be more for me than for her. So, you see, while I could justify it, I've been able to see where MY problems are, and acquiring an AR for her over something else she would like/ want/ use more would be a foolish gesture.
OP, I obviously don't know anything about you other than what you've posted in this situation. I don't know your financial situation, your gun budget, her wants needs and desires, or if they are being met. In my case, I sell stuff I don't use to fund purchases for guns. We simply don't have the discretionary funds to purchase guns, and our arrangement is kosher. I have admitted to myself that I had a problem and it would eventually drive a wedge between my wife and I. With my first wife, I was at the point where I no longer gave a crap if we split up. We were too different and no amount of counseling or attitude changes would change all that. This time around, I don't want to make the same mistakes. I've already made some of them, and I hope I can catch myself in time to stop and make amends.
I have to agree with the prospect that your zeal for defending your family (and owning the guns to do so) might be a driving force for losing what you zealously stand by to defend.