No not without protection if you must have sex with this person, you should always protect yourself, they may have a different strain of the virus than you.

If someone is DETECTABLE and their HIV strain is resistant to your medication keeping you undetectable, then YES you CAN become reinfected and create a new strain of HIV. The more reinfections you get, the less options you'll have for medications to a point where there could be no medication that will help at all.

https://www.verywellhealth.com/hiv-reinfection-...