Depends, was itoral or anal?
Oral no worries. Anal no risk for HIV if he is truly undetectable and less of a risk for the top if he isn’t
If he is truly undetected being on ARV drugs the risk is minimal.
However, you had unprotected anal sex with an HIV positive person, it will be essential for you to test at 4 weeks with a Duo for your own safety. If you wish to get a 100% conclusive you will have to retest at 6 weeks. A 4 weeks duo changing ahead is very unlikely.
Good luck.