How can I stop someone who I thought was my friend from spreading the bad thing that i did,such as kissing an older man that I was not married to or does not have any right to touch?

Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

First of all, repent to Allah and adhere to His obligations and avoid His prohibitions.  You should also do as many good deeds as you can.  Allah Says (interpretation of meaning): {And perform As-Salât (Iqâmat-as-Salât), at the two ends of the day and in some hours of the night [i.e. the five compulsory Salât (prayers)]. Verily, the good deeds remove the evil deeds (i.e. small sins). That is a reminder (an advice) for the mindful (those who accept advice). }[11:114].

You may also stop this companion by warning her against the punishment that Allah inflicts on those who follow up the mistakes of people and spread them.  Allah Says (interpretation of meaning): {Verily, those who like that (the crime of) illegal sexual intercourse should be propagated among those who believe, they will have a painful torment in this world and in the Hereafter. …..}[24:19].

The Prophet (Sallallahu Alaihi wa Sallam) said: “Do not harm Allah’s slaves, do not criticize them, and do not try to reveal their Awrah.  Indeed anyone who seeks to divulge the Awrah of his Muslim brother, Allah will – undoubtedly – divulge that person’s Awrah in his home.” [Ahmad]

Remind her of the Prophet’s (Sallallahu Alaihi wa Sallam) Hadith that urges Muslims to cover other Muslims’ faults and sins.  The Prophet (Sallallahu Alaihi wa Sallam) said: “And whoever covers a Muslim (by not uncovering his/her sins) Allah will cover him/her in this world and the Hereafter.”

In conclusion, when the Muslim notices some shortcomings of his/her Muslim brother/sister, he/she should advise him/her and admonish him/her but never divulge his/her secrets.

Allah knows best.