All praise be to Allah, and may his peace and blessings be on the last and best prophet and messenger, Muhammad.

It is a horrible sin, yet not the zina that is punishable with hadd.
If you were involved in this, I urge you to repent promptly and seek help from Allah through fasting (if you can’t get married).
If you can get married, that would be the best solution, and remember that the less burdensome the marriage is, the more blessed it will be, as our beloved Prophet (May Allah bless him and give him peace) taught us.
If you can’t get married and couldn’t suppress your lustful desire through fasting alone, it will be better for you to masturbate than to commit that sin.

May Allah help you on yourself and the shaytaan, purify your heart and guide us all and protect our Muslim sisters and daughters.