The way to not "cheat" and legit go for "true ending" is to click the exploration map (or trading map), click your own pub. it should bring up the skill tree. purchase the furthest icon on the right, second row from the top (The icon should look like a piece of parchment with a eye icon on it). It should cost about 1000 gold? for first upgrade that enables you to buy a new npc "whore" so you can do H scenes without exploiting your own girls. Unfortunately, NPC whores generate "shit" sex points for the skill tree, it's a price you pay. but doesn't really affect much, so long as you don't go full out NTR. Buy as many whores as needed, budget yourself (it gets real expensive real quick, because debt repayment is expensive).
Don't try to aim for two heroines at once, since you can only confess to one of them (the game blocks you after you confess to one). And you should save scum before next day, just in case the girl gets cock blocked by the chef and you waste a turn. Why does wasting a turn make a difference? Because horniness matters, you want to avoid reaching 999 horniness to avoid your girl getting boozed up and fucked (unless you want to cheat and turn off drunk sex, which makes it impossible to NTR at 999 horniness). Horniness builds up slowly during turns. Also, use the other heroine to "help" the chef cook, don't use your main heroine (which one girl you wish to confess to, is your *main* heroine), cooking causes intimacy with the chef to rise, and you don't want that, but NPC whores cannot help you cook, so you need to use the "useless" heroine.
Useful tip, to avoid 999 horniness and drunk sex, use the first option during DATING turn, and the last option. It feeds your heroine the horniness removal drug. It's 500 gold for the first potion, 2500 the second one.... It gets expensive super quick, so you would only feed that potion at about 800-900 horniness, and also only for the confession girl.
Here's the tricky part, confession requires 500 affinity points and... 900 horniness. So make sure you do your calculations properly and don't overdo it and cause a drunk sex. So save scum hard, and plan ahead.
Oh, and remember to pay your debt to avoid getting owned by that debt collector, although I think that one is pretty obvious.
Since I mentioned NPC whores give shit sex skill points generation, whenever you don't need to cook meals, you can pimp out your "side" heroine girl. Just don't fuck up and select the confession heroine.
Also even if you confess to your heroine, do NOT pimp her out afterwards. Just because you confessed to her and fucked her, if you even do a single sexy event with anyone else, the pregnancy fails. You can check if the pregnancy fails, if you have sex with your heroine, your MAIN CHARACTER will wear a GREEN CONDOM.
Sort of helpful hint for near end game players, don't buy the skill tree second skill from the right, on the bottom row. It's the icon with some indian turban guy (not the cloaked one with face mask). That's the "noble" customer increase skill tree. If you buy it, nobles appear more often, then you have to play this stupid mini game (SUCCESS heart icon on the top left, during PUB turn), and it's up to RNG whether or not your "Confessed" heroine gets picked as the game player. If she gets picked as the player, and loses, it still counts as betrayal and it fucks up your pure route. This is the problematic part, if you IGNORE the mini game altogether. There is a hefty fine of gold and honor, and you can't sacrifice your side heroine to block the nobles, since the nobles pick which girl to play, not YOU yourself.
Love this game, except I wish there was more commentary when they get fucked during the nobles mini game... It's a three some, but we never see or hear any commentary about the heroines downfall. The only commentary about their downfall is the one liners they say during the rock paper scissors game, but they don't say anything after the sex starts behind the curtains. Bummer, a real wasted chance.