Tu hija se está por casar con un buen hombre.
Your daughter's about to get married to a good man.
Caption 17, Provócame - PilotoPlay Caption
When Patricia says to Ignacio, Tu hija se está por casar con un buen hombre she is saying, "Your daughter is about to get married to a good man." Estar por hacer algo can be interpreted as "to be about to do something." Note that the reflexive pronoun se in Partricia's phrase belongs to casar, not estar; she could have just as well have said Tu hija está por casarse.
Está por llover.
It's about to rain.
Se descompuso, pero ya está por llegar el Doctor Regiano.
She got ill, but Doctor Regiano is about to arrive.
Caption 40, Muñeca Brava - 33 El partidoPlay Caption
Estábamos por comer.
We were about to eat.
Provócame is an Argentine program. In some Spanish speaking areas (not Argentina) estar por + infinitive can indicate an inclination to do something, or to be in the mood to do something. Likewise, in some (other) regions, estar para + infinitive is the more common way to indicate that an action will soon take place.