You shouldn't ask for codes. Instead, you should develop your skill. Games are more rewarding if you work at them. That doesn't mean I won't help, though. So I offer a Survival Guide for Dating Sims.
Visualize your character. Is he a Criminal, Charmer, Serious Mind, or Casual? Charisma gets the ladies, but offers low-paying jobs and requires bar-hopping to "train". Strength gleans "high-risk, high-return" jobs and impresses women somewhat. Knowledge gets little respect, but offers solid, well-paying jobs.
Prioritize training and finances first. Shopping and flirting come later. If the Sim has "test your prowess" mini-games, these provide alternatives to normal methods of training.
Once the money flows, become a bar-hopper. Drinks are on you (does he honestly spend twenty dollars worth of booze on himself?). Learn to socialize and flirt there!
With Charisma, she opens up. Ask her name to become a "New Friend." Gifts can be offered--they come in three types, and they're all important (some will work better during some dates as opposed to others). After "New Friend" comes "Good Friend," where you'll get to call her. Note: if you carry your phone with you and she calls you, answer it quickly or lose Relationship Experience!
Being a "Close Friend" lets you date her. Write down everything she says about herself. On a date, you are quizzed about what you know. Answer correctly! Combined with the right gift (if any) with a high Relationship Exp. level, she'll start blushing. NOW hit the Kiss Icon--NOT before.
Once she is your "Girlfriend," she talks about more personal matters. Write these down--devote whole days to flirting with her! You also get to tour her house or Love Hotels--and the dating venues are expanded upon. One game features an expensive date (they all cost money) out in space, and you come across a device that relays all her vital stats to you!
Eventually, you'll become her "Lover." To score, profess your love and your readiness to bear the consequences. A long version of a date quiz commences and, if you come out on top, you're granted the password you seek.
A few last notes: her mood is depicted by her face--if it looks odd, she might need coffee (when tired), or medicine (sick), or a handkerchief (crying). Purchase those items ahead of time. In Sims heavy on mini-games, these items often serve multiple purposes.
That's the best I can do with a 6,500 character limit. I hope you find it useful.