Being a US Marine duped by girlfriend?

I met a girl 3 months into the relationship and we decided to get engaged prior to my deployment to Afghanistan. For four years I have been sending almost my entire paycheck to our joint account. I discovered upon my return that she had a son with some guy and she had been putting him through college to become an accountant with my hard earned money. What can I do? I have nothing to show for for the hardship I had gone through. What can I do since he they are going to have an affluent career off my back and I have nothing to show for.