Please do not do that. If you put the NTR tag there, the NTR fans will be expecting NTR contents when they click on your game. It will be a miscategorization in doing so and even a bit disingenuous. The scenario you have in your game is straight up netori since Brad will be the one being cucked by the MC if Sarah is a love interest.
When you put the [netorare] tag there, you are saying that there is NTR contents. If you do not plan to add anything in regards to NTR as you have commented, you better put a huge warning label to the NTR fans because they will come asking.
A word of advice: there are just some people that just can't handle any aspects of real life showing up in a game. For example, you may be dating a person who already have sex with another person. They will come screaming at you about NTR, but you need to make sure that before you start pleasing one crowd over another, and before you slap on any tag, contemplate on whether it belongs or not based on the contents in your game, not because somebody defined NTR as "all the women can only belong to the MC."
I have played a lot of VNs and good VNs make the characters feel real with their own lives and personalities. Don't just create lifeless, stock characters thrown in to please the MC. Don't just create a porn simulation because yours will then also join the multitudes out there and just drowned with them. Try and make your game stand out.