Are you always a deacon once you are ordained as a deacon?

No.The bishop is the one who validly confers the Sacrament of Holy Orders. As the Catechism of the Catholic Church states:1576 Since the sacrament of Holy Orders is the sacrament of the apostolic...

a deacon in the catholic church are like priests but only they don't get payed and they cant do everything a priest does

Yes of course as like with anything else they may not have only attained a personal goal but a spiritual one as well.

Emeritus - (revision September 13, 2005) The Emeritus Deacon category was adopted in 1987 to honor those deacons who have given outstanding, meritorious, and loyal service to the church and to the...

He should be able to perform marriages if he is authorized by the state where he lives