Based on the small amount of information provided, it seems possible that your daughter may have been sleeping with your partner. It’s also possible that either he or she were watching pornography and that’s what you heard in the phone recording.
You mentioned that he acquired an STD that he did not get from you. That would suggest that he was sleeping with another person, perhaps your daughter. If it was your daughter, she may also have an STD. You might try asking your daughter if she has the same STD as your partner.
Other than continued surveillance, there may be no good way to know what may be happening between your daughter and your partner. The fact that you think it realistically possible, that your partner slept with your daughter, reveals significant potential problems in your relationship. If you suspect it to be true, then it would seem unwise to leave them alone together.
Logically, either your partner is sleeping with your daughter or your partner is not. If they are sleeping together, you have a problem. If they are not sleeping together, you have a different problem. If they are sleeping together that means you cannot trust your daughter or your partner. Those problems must be rectified.
If they are not sleeping together then the problem is that you seriously suspect both your daughter and your partner of doing something of which they are completely innocent. This would speak to a trust issue or even paranoia, on your part. It is important to find the truth because either way, the problem must be rectified. Counseling would be a very good place to explore this problem and to help you to find your answers.
Thank you for your question. Good luck.
Dr. Kristina Randle