From my experience, none of us can really give you advice with it being the right choice because we don't know how your relationship works.
For example:
I'm 21. My fiance is 28. He is not an affectionate guy, and isn't really the holding hands- saying I love you kinda person. But, he shows he me he loves me by other actions that may not seem like anything to some people, but he knows what's important to me.
Like with fish- by the time I get paid, and pay my bills, and put gas in my car, I have maybe $10 to my name- this has to last me 2 weeks until next pay. So I never have any money to spend on other things, but he does... So we discuss the fish in question, and then we normally make a trip over the weekend to get said fish.
He's got a 72 bowfront calvus tank.. I have a turtle tank. He's got a 150 Frontosa tank... I have a 125 community tank... He has a couple of cichlid grow out tanks, and I have my puffer tank, sturgeons, and shrimps...
We share a 180- some of the fish are mine, and some are his. We also have a 240 with rays. 1 of the ray is mine, and the rest are his- but, the ton foil barbs are mine.
He does the tank maintenance, and I make sure they are healthy, and fed- and treat for any issues.
***Why not sell a fish or 2 in the tank- make some room, and add 1 fish of her choice- but explain that if it causes any mishap it goes back to the store. Not only does it show you have "spine" it shows that you care about her wants, and you can compromise.