I'll interject my two cents -- and bear in mind I'm not a trained relationship counselor or therapist. IMHO only!
I always start from the premise that not everyone MUST own a firearm. Whether for religious, personal, political or other reasons, some choose not to have anything to do with them. That's their wish, and I can respect them for their opinions. I only ask that they respect mine. So long as neither one of our actions affects the others...we should be good.
When you have a situation where one person in a relationship is looking to expand into a new area - whether it be professional, religious, hobby, etc...and the other is objecting to it, tread lightly. Personal relationships can take real damage if the decision-making isn't done correctly and jointly.
When I was newly "into" handguns, I purchased my first one over the strenuous objections of my partner. We'd argued about my purchase prior to it for the previous 6 months. It became an extremely sore subject. I just went ahead and "did" it...indicating that my way was right, and she was being paranoid and should get over it. After I woke up from the coma - I decided that wasn't the right way to go about it...
After not speaking for several weeks, I approached her with the topic again - her chief objections were the safety of our children, and that handguns were inherently dangerous. I started by reinforcing my safety precautions - firearm and ammo stored separately, under lock and key, etc, the fact that I'd be training with it regularly...and that I would be bringing our children up to respect and use firearms safely. We reached an armistice, whereby the pistol could stay, so long as it was safely stored, and not in a place where the children, or their friends, would come into contact with it w/o me present. The experience taught us to lay out the discussion in diplomatic terms, not belittle or become condescending to each other...and to listen instead of speak.
Now, fast forward 4 years -- I wanted to obtain my carry permit. I started the discussion, and not by presenting her with a handgun on my hip and a newly laminated permit card. I presented my pros, she presented her cons -- and again, her focus was on safety. We agreed on a lock box for the cars, and that the firearm would never be "left out" on a counter, etc...if that were to happen...*insert hell breaking loose comment here*
Fast forward again to today -- she discreetly jokes about me carrying a firearm to close family and friends (which I'm ok with), and made a comment once about how she was glad I had a gun on me. She did make a passing comment about not noticing how the pistol collection had grown. She has fired nearly every one in the "arsenal" and enjoys being a good shot even though its not "her thing".
We still don't agree politically though -- that's a discussion for another day....funny when a Libertarian marries a confirmed Liberal....
Edit: Bottom line, they can arrive at a common ground that both can respect - and don't necessarily have to change each others' minds.
Nothing to see here. Continue swimming.