People can and do change their religion. This is simply a fact of life that we must all deal with. Our own children may leave our religion and convert to another religion. It happens all the time. Only a fool would deny this.
Some people change religions because of marriage.
They fall in love with a person of a different religion and they give up their religion to marry that person. It happens all the time. Other people change religions due to coercion such as threats or violence or bribes of money, sex or political advantage. If you change your religion because someone threatens to kill you if you do not accept their religion, this is not good. If you convert to a religion in order to obtain money, sex or a job, this is not good either.