i feel like there might two reasons why people end up being sex-negative

1. they never had proper sex education. it's basis of sexual confidence. it means that sexuality shouldn't feel dirty, awkward, wrong, pathetic or shameful.

2. they have unresolved sexual trauma. they think that sexuality is bad when in reality, it's the people who didn't respect your boundaries.

talk to sex therapist or sexologist. in my own experience, they're much better handling with sexual emotional baggage than regular therapists.