EX not abiding by the separation agreement

In our separation agreement my ex said he would be responsible for a loan in my mother’s name. His credit was bad and I was out of work with pending disability. She agreed to give us a loan in her name if he paid it in full. He agreed in writing and again in our separation agreement. He has failed to pay the loan at times and late on others. He now is not wanting to pay at all since I found out about the bigamy and turned him in. So, what can I do? The separation agreement also says that if something is not being done, that the person at fault would have to pay both attorney’s fees. Will a lawyer take the case with relying on him to pay them instead of me? If not, can I file on my own and what is the procedure?