How will i know if the marriage is valid or not

i have a friend and he was marrried on his daughter's mom. they've been seperated for almost 5 years, now he wants to confirm if that marriage is legal or not because his wife has been bugging him asking for too mucb money even though he's been giving financial support for the child but his wife wants more than he's giving becoz she said that she needs to pay all the bills and her parents dont have enough money for it, and if he ever gets late for sending the money shes always blocking him, she even blackmail him that if he didn't send money he'll never see his daughter again, that when he decided to do some action..
here's what happened he's supposed to work abroad but before his flight the family of his gf wants them to get married for "assurance" he's only 21 at that time and her gf is 25 because of the sudden decision he disagree and told them that maybe they can get married by the time he goes back from working abroad but they didn't agreed so 2days before his flight they got married (its only a civil marriage) he don't have any guardian who attended or a witness from his side so basically its all from the side of the girl, and the one who signed for his guardian is the aunt of his gf who works at pao (public attorneys office) in the municipality. and after 2 days he works abroad until now at first they've been communicating just fine but as month pass she would always ask for money so they decided to just broke up but the support for the child will be continued. i just want to know what's the right and first thing to do. thank you so muh who ever will answer this.

first have it checked with the nso if there was indeed a marriage contract registered. second may i know when was he married because under the family code there are different essential and formal requisites for the validity of marriage which can be a ground for annulment later on if he so desires to file one.

thank you so much for answering.. he haven't check yet in nso but i already told him to check, it was march 21 2011, he's 21 at that time they didn't attended any seminar for the marriage and the one who signed for his guardian is the auntie of his wife. even though he refused to be married at that time they still insisted to make it happen so they rush everything before his flight abroad.