D'Andre - I'm much older than you and I"m on my second marriage (10 years and counting, though!). Perspective on money/finance is one of the biggest influences on a relationship, so please have these critical conversations now before you get married. But let me share how I eventually got my husband to come around on all this real estate investing stuff.
I have been bullish on REI for years now (I did a 1031 exchange using a condo I owned before I met him - now a 4BR/2BA w/ 5 renters) but he would always disparage my decision saying it was a 'bad' investment. I figured out that he was comparing REI with stock market investment (he used to sell bonds) and he was just looking at it from the perspective of cash on cash gains. Once I knew what his baseline for comparison was, I focused on how REI had advantages over stock market investing. Granted, we do both but the conversation is about diversification. In the end, we found common ground on the REI goal of cash flow using cash on cash analysis. I also pointed out the differentiators for REI over the markets:
1. tax benefits (expenses, depreciation)
2. tangible & incoming producing asset once mortgage is paid off (showing him amortization schedule mapped to rental income helped)
3. Regardless of political and market factors, people will need a place to live and small, affordable rental units will always be in demand.
So my perspective on your situation would be to:
1. Have the conversation ASAP and if needed, get a 3rd party facilitator to help with the discussion. If anything, they can make notes on where you align and where you still need to work through issues.
2. Ask your fiancée to articulate her perspective on growing wealth and how it relates to quality of life (time, health, family, etc.)
3. Based on 1&2, frame your proposal in the context of what has meaning to her and find common ground on one strategy.
GOOD LUCK and kudos to you for having such foresight at a young age! I got married very young the first time and I didn't think about any of this back then.