My girlfriend of 18 months and I had unprotected sex. She became worried that she had contracted an STI, despite having no symptoms. Although she was never accusatory, she became unwilling to have sex. The results were negative, but then she became convinced she was suffering from genital warts. She now feels she "can't have sex while this virus might still be in my body". We have satisfying non-penetrative sex – but should I worry about her?

Some STIs can indeed be present without obvious symptoms. Concerns about STIs are always valid, and the worries that are expressed by a partner should always be respected. But you have picked up on the possibility that there might be another issue here, or another motivation for avoiding penetrative sex – and you may well be right. Perhaps non-penetrative sex is more enjoyable for her, as is the case for many women. Have a frank and open discussion about her preferred styles of sexual contact, and what best leads her to orgasm, and you may receive some important information. But mood disorders can also affect sexuality, and it is also possible she may suffer from anxiety, or a related problem to do with being over-anxious about her health. If you think this might be true, help soothe her and gently suggest she takes steps to address her general anxiety, which will affect more than just your sex life.

• Pamela Stephenson Connolly is a psychotherapist who specialises in treating sexual disorders.

• If you would like advice from Pamela Stephenson Connolly on sexual matters, send us a brief description of your concerns to private.lives@theguardian.com (please don't send attachments).