Do I HAVE to Go to Confession?

Do I have to go to confession? Yes.

The council of Trent says: "As regards those who, by sin, have fallen from the received grace of Justification, they may be again justified, when, God exciting them, through the sacrament of Penance they shall have attained to the recovery, by the merit of Christ, of the grace lost: for this manner of Justification is of the fallen the reparation: which the holy Fathers have aptly called a second plank after the shipwreck of grace lost. For, on behalf of those who fall into sins after baptism, Christ Jesus instituted the sacrament of Penance, when He said, Receive ye the Holy Ghost, whose sins you shall forgive, they are forgiven them, and whose sins you shall retain, they are retained. Whence it is to be taught, that the penitence of a Christian, after his fall, is very different from that at (his) baptism; and that therein are included not only a cessation from sins, and a detestation thereof, or, a contrite and humble heart, but also the sacramental confession of the said sins, at least in desire, and to be made in its season, and sacerdotal absolution...," as well as, "If any one saith, that he, who has fallen after baptism...is able indeed to recover the justice which he has lost, but by faith alone without the sacrament of Penance...let him be anathema."

The Church makes it clear that the sacrament of penance is necessry for salvation after having commited mortal sin.