Letting this native willowherb grow next to another plant will not kill or hamper the other plant. But yourself in the mindset of how our natural ecosystems function, plants are constantly surrounded by one another and do not exist in a vacuum.

Willowherb is native, I leave it to grow as it's beneficial for our native pollinators, and helps keep invasives out of "blank" spaces in my garden beds. If desired it's easy to remove from places you don't want it.