Broad strokes :
You have a deck, separated by suit. You have one card of each suit as your ‘stat’ (eg, Work income, Affection, Cooking Skill, Lifestyle Comfort). Each day you draw a random card from each deck, which is the number of reps you need to do in four specific exercises (eg Push Ups without stopping, Four Count Sit Ups, half-kilometer of rowing per point, lunges). You can keep your current card or swap it with what you drew before the workout. Higher numbers are obviously IRL harder, but provide the fictional avatar, the MC, more ‘power’ for the day.
Each playbook details a specific potential love interest or plotline (and dictates which exercises align with which suits). You have a ‘core page’ each real life day, where after the workout you update your consumables (money, energy, etc), then decide how to spend them, limited by your stats. On certain days, or when a certain stat level is first hit, you turn to a specific page and get some plot, make a Choose-Your-Own-Adventure style decision, maybe get some art. Preferably fold-out, so you don’t accidentally spoil things early while flipping through looking for specific pages. Sometimes these might change your Core Page - maybe you’re on vacation, which gives you different daily options and has special cash-draining rules. Maybe she gets the flu and you have slightly different options accordingly.
Your significant other also has some stats that your choices slowly grind up, but that also get nudged by bespoke single-instance events or choices that pop up when a given metric gets met.
Fail conditions exist too - probably end up breaking up if your skipped days exceed a given value, or you get assigned an undesirable core loop for failing a certain number of workout events (that requires hitting another, separate sub-goal to escape from).
So… basically “The Weighting Game” or “Tramp” or “Fill Me Up” influenced gamebooks (life sim + VN style instances at given points) that use the player’s willingness to work out as a currency. If I (or someone?) got a solid single instance of this, one that actually worked in play and was entertaining, then spewing forth alternate playbooks would theoretically be a lot easier than developing a whole game from scratch.