Why don't I feel pretty or sexy anymore when I'm with my partner?
I have genuinely no idea; I am not psychic!
Think about what usually makes you feel sexy, and ask your partner for more of that! Whether it's flirty touches, compliments, specific types of sexual behaviors, etc. Sometimes couples just fall into a 'routine' and it can take some intentional effort to re-ignite the sexy spark. But you gotta identify what creates that spark for you!
Consider getting a bit out of your comfort zone and trying something new together, like taking sexy photos, shopping for a new sex toy or lingerie, getting a couple's massage, going to a sexy event together, sexting each other, etc.
Consider what else might be affecting your sense of self and what you can do to improve your self-esteem independently of your partner. I often feel less sexy when I'm tired or stressed, so think about whether therapy, a lifestyle change, or just some patience through a tough time could help. Some people really enjoy how they feel about their bodies when doing dance, yoga, or martial arts.
If, after you've tried talking to your partner, putting some effort into re-igniting that spark, and finding your inner sense of sexiness, you still feel like this around your partner, it might not be a healthy relationship to stay in. Partners should make you feel precious, cherished, and wanted - and if your partner can't or won't do that, that's not okay.