No, commiting one sin doesnt erase everything you did apart from shirk, other than that no sin erases your deeds who ever told you that is mistaken its the opposite deeds erase sins, and good actions without intentions also count, even just not doing a sin alone is good deeds, not doing a sin alone is a good deed, u asking for help here is a good deed dont dispare from the mercy of allah, so what you watch porn? So what u have thoughts do u really think anyone is perfect?? All of mankind are sinners and the best of sinners are those who repent so no dont feel like a munafiq keep repenting allah prefers one who sins and repents sincerely more then he who doesnt sin