Have I deflowered my relative whom I sexually harassed in her childhood, and what are the legal consequences for me?

If the sin occurred before puberty, then there is no sin upon you, for the Prophet, peace and blessings be upon him, said: "The pen has been lifted from three: from the sleeper until he awakens, from the child until he reaches puberty, and from the insane person until he regains his sanity."

If it occurred after puberty and then you repented with a sincere repentance, then repentance erases the effect of the sin and removes the description of disobedience from the penitent, for he, peace and blessings be upon him, said: "The one who repents from sin is like one who has no sin."

Repentance involves abstaining from the sin, regretting having committed it, and resolving not to return to it. You must conceal yourself and that girl, and it is not permissible to tell anyone what you have done, for the Prophet, peace and blessings be upon him, said: "O people, it is time for you to cease transgressing Allah's limits. Whoever commits any of these abominations, let him conceal himself with Allah's concealment, for whoever exposes himself to us, we will apply the Book of Allah against him."

It is recommended to hasten to marry if you are able to, and not to pay attention to intrusive thoughts.