I don't think it makes you a bad mum at all!
I commuted more than 45 mins to school everyday for all of high school, my sister did it for HS plus half of PS. It really isn't that far at all - are you sure there is no way to keep your current arrangements? Either way, sounds to me like you are in a fabulous position to be able to pursue what makes you happy and you should do that!
I think the thing nobody speaks of much is that kids are only PART of you and PART of your life. Doing the best for them often means doing the best for you, and in the short term, that may be contrary to our perception of social norms. Being with their dad is no different to being with you - he is a loving, attentive, responsible and connected parent too.
Good luck! x