In 1995, Mateo was waiting tables at the Valley Inn.  He was walking on the beach one day when he noticed a beautiful woman wearing a wedding dress being hassled by some thugs.  The woman turned out to be Hayley Vaughan, and that rescue was the beginning of their relationship.  Hayley had run away from her wedding to Alec McIntyre.  They were soon reconciled and the wedding was back on, but Adam asked Mateo to keep an eye on his daughter, as he didn't trust Alec.  Turns out the mistrust was well-placed, as Mateo saw Alec flirting with Hayley's mother, Arlene.  Hayley and Mateo had some real chemistry, and soon they were sneaking little kisses in elevators.  Hayley, confused and pressured, eloped with Alec, but she and Mateo discovered her new husband forcibly pouring whiskey down her mother's throat.  Alec went to jail and Hayley and Mateo began spending a lot of time together.

Mateo's family wasn't sure that Hayley, twice-divorced and a recovering alcoholic, was quite the right gal for Mateo.  Hayley wasn't entirely convinced either, but after the return of high school beau Brian Bodine, Mateo backed off and let her make up her mind.  She chose Mateo, and they became engaged.

After the death of Hector Santos in a car accident, Mateo became the head of the family.  He and Hayley purchased Hal's Bar and renamed it Holidays, and they made plans for the future.  There was a detour, however, when an old friend of Mateo's, Tanner Jordan, turned up.  After flirting and maneuvering, Tanner drugged and took advantage of Hayley one night.  Hayley finally remembered the event and confessed it to Mateo on their wedding day, causing Mateo to call off the wedding.  Eventually Mateo discovered the truth, rescued Hayley from Tanner (who wound up dead) and they were married in the spring of 1997.

The joy was, of course, short-lived.  In 1998, Hayley was kidnapped and given a toxic-paint tattoo by Lee Hawkins, who also burned down Holidays.  Mateo rescued her once more, but the paint damaged her liver, and Mateo and Hayley feared they might never be able to have children.

Hayley and Mateo were planning to renew their vows when Raquel, Mateo's first wife, appeared with his son Max and announced that she was still married to him.  Raquel tried to win Mateo back, but he was true to Hayley.  She got a good report from the doctor and they planned to start a family of their own and, meanwhile, opened a new club, The Sounds of Salsa.  Raquel agreed to give Mateo a divorce, but Max was unhappy about that and Hayley and Mateo decided to put off their plans for a while.  Hayley was starting to crack under the Raquel/Max pressure, and decided that in order to maintain her sobriety she needed to move out of their apartment.  She did, and began a flirtation with friend and employee Ryan Lavery.  It didn't come to anything, though, as Hayley realized she and Mateo were meant to be together.  They were married in the spring of 2000.

Since his marriage to Hayley, Mateo has been concentrating on the club and keeping an eye on his scheming mother-in-law, Arlene.  When Arlene turned up pregnant by husband Adam, Hayley and Mateo made plans to adopt the baby.  Arlene miscarried, though, supposedly during an argument with Liza, leaving Mateo suspicious about Vanessa's part in the tragedy.