What is the ruling on shaking hands with a non-mahram woman, kissing her, and sucking a man's penis until ejaculation? Is this act considered Zina (fornication/adultery) or one of the major sins, and what is its expiation and the way to seek Allah's forgiveness?

The questioner must sincerely repent of the abominable act committed, regret it, resolve not to return to it, and adhere to Allah's law by performing the obligatory duties, avoiding prohibitions, and frequently performing good deeds that expiate sins. The questioner must also stay away from the causes of falling into such acts, for they are among the gravest sins and lead to indecencies.