You would need to contact the benefits department of the branch of military he served in. If he has retirement, they will need a copy of the divorce decree.

What if we are still legally married but he has a girlfriend that he lived with and they had two kids together this year

You can't get any retirement funds he may qualify for until he meets retirement age. He did not retire from the military if he was less than honorably discharged after just seven years for the crime he committed. He may qualify for no benefits now, as I recall you have to serve 20 years to qualify for military retirement benefits. You'll have to call and inquire if you or your children qualify for anything during a transition period, most likely not if he was involuntarily separated due to the crimes he chose to commit.

His having children out of wedlock has nothing to do with this, really. You can't still be legally married if you have a signed divorce decree. Are you still married or not?

Yes we are still legally married i have filed for divorce three times now and he refuses to sign the papers since he was overseas he was protected by the soldier sailors act and i couldnt have him officially served but now he is back in the states so im going to do it again

If he was discharged dishonorably (which I assume he was based off the fact that he was in federal prison) then he most likely lost any retirement benefits he had and if he lost his benefits then there would be no benefits available to you.