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Am I in the wrong for bathing my brothers gfs dog?

So since the dog was a little puppy I've always been with him most of the time bc they barely are ever home. If I can say how often he is with them it would be like every night at least but during the day he's with me and my mom who take care of him. Anyways I noticed the other day as I was petting him that it was bumpy at the base of his tail and yeah it was fleas. So disgusting, I love this dog and like to keep him in my room or on my bed but I don't want to touch him if he has fleas all over so I took him a bath and even applied flea drops and that helped so much. He had so many fleas that they were even still alive in the bathtub and around it trying to jump on my legs afterwards. Well this morning, 2 days after I gave him a bath my bros girlfriend was knocking nonstop on my door telling me how she appreciated me giving him a bath but I'm "messing up his schedule" I'm assuming they bathe him once a month and they have multiple dogs + other pets that they barely can take care of but anyway. I just wanna know should I feel bad? If I leave him alone that poor dog is gonna suffer with no attention or help since I'm the main one he's with through out the day. I know he's not my dog but I feel bad to just ignore him like that. I don't know what to do
Am I in the wrong for bathing my brothers gfs dog?
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