Does he have to marry his female relative whom he touched in a haraam manner?

No File Exists
Check below answers in case you are looking for other related questions:
What if her brother is her wali and he entrusts the matter of her marriage to her maternal uncle?
Obstacles to a Christian woman marrying a Muslim man

No File Exists
Related Answers:
Woman's right to refuse marriage to someone
A realistic look at marriage to women of the People of the Book
The fact that the woman is older the man should not prevent them from getting married
What if her brother is her wali and he entrusts the matter of her marriage to her maternal uncle?
Obstacles to a Christian woman marrying a Muslim man

Recommended answers for you:
Etiquette of Eid
Ruling on husband and wife playing while fasting
The reason why it is forbidden to have intercourse with one's wife when she is menstruating or bleeding following childbirth
They committed zina then they got married, and they are asking whether the marriage is valid
The difference between zakaah and sadaqah