Hi dear, I have understood your concern and I will suggest you the best possible treatment options.
Next Steps
In any sexual relationship, mutual trust and understanding is the key. As there is no such test available to detect any previous history of sexual activity. The only thing that I can suggest you is to be in good conversation with your partner and get your doubts cleared.
Health Tips
If needed, you can get counseling done from expert in the field.
I hope this answer helps you.