Citronella in Green Tea

I take my green tea with a few leaves of citronella. Since I drink about one and a half liters of it a day, I wonder if it is a bad thing?

Because "citronella" can mean several different plants it is important to establish exactly what plant you are referring to. I suspect that your "citronella" is what we call "lemon verbena" and known botanically as Aloysia citriodora. However, "citronella" is applied also to a type of lemongrass (Cymbopogon spp.) and even to lemon balm (Melissa officinalis), and probably to other plants in different regions of the world.
If your "citronella" is lemon verbena or lemon balm, there is no evidence that either plant is harmful when taken with tea in the manner and quantity that you describe. If your "citronella" is one of the lemongrasses you need to be sure which Cymbopogon species you have. For example, the true lemongrasses C. citratus and C. flexuosus are safe to take, but the true citronella, C. nardus, is used as an insect repellent and may not be appropriate for long term consumption.