Of course you're not a bad mum!

As has been said, you do what you do, and once it becomes "normal" it's not necessarily difficult to thrive in that role. there are many MANY single parents out there doing similar to you, and they all say "it's just what i do". i think the longer you do something (and you've been doing this for quite a while now) the easier it becomes. if you're used to having support (from a partner) and they it's suddenly withdrawn, then yes, it's going to be a whole lot harder to accept and thrive in that situation kwim?