Drinking Tea can help with weight loss if it's drank without milk.
Milk is fattening and can cause you to gain weight if you drink enough of it so yes drinking too much tea with milk included in the tea could cause weight gain instead of weight loss.
So if you're trying to lose weight when drinking tea then it's best to avoid adding the milk to the tea because like I said tea can indeed be fattening if milk is added too it.