Does practicing perversion in childhood, such as that which the people of Lot used to do—God forbid—affect the validity of a marriage contract in adulthood? And is the anus the same as the anal opening?

What you have done is a great abomination, and it is obligatory to repent sincerely from it. However, as long as it did not involve direct anal penetration, it does not necessitate the prescribed punishment (حد), but it is forbidden and a precursor to sodomy. It is advised to seek forgiveness (استغفار), perform good deeds, adhere to supplication (دعاء), disregard obsessive thoughts (وساوس), and consult a trustworthy psychiatrist if the obsessive thoughts persist.