Let’s talk about what people commonly talk about regarding what kills the passion. Even better, you can put in comments or email me at firstname.lastname@example.org telling me what kills the passion for you. Let’s do both, okay?
“Not trying” is the biggest killer because people feel taken for granted, underappreciated and not a priority. You just have to flirt, tease, banter etc. You can’t stop doing nice things or stop learning about one another. Look at their love languages, their gender communication, what their specific personality needs are etc. and keep tuning in. Keep building rapport and emotionally connecting. Connect on every level you can, actually. Don’t tell her that you are valuable, show her your value.
Make sure you are equals, too. If either of you does too much for the other without reciprocation, that is not good. Talk about it rather than doing it with resentment. Some people try to over accommodate or impress their partner. When you try too hard, it feels needy, which destroys passion. Talking too much about your failures can also scare people away. It is good to be open and vulnerable, when it is in balance with being strong and able to stand on your own two feet. When you are stuck, do you get help to get unstuck or do you adopt a victim mentality? Are you able to take care of yourself, your job, your car, house etc? Do you signal future stability by demonstrating your ambition, your initiative?