Roy,
The answer is yes, demonic possession could pass from one person to another through intercourse which is essentially the two becoming one.
If you have been involved with someone you fear to be under demonic influence, of some sort, you should seek the sacraments of Penance, the Eucharist, and consider fasting as well.
Pray the Rosary and stop fornicating and committing similar sexual sins if you want to be free from the evil that follows.
Peace,
Bob Kirby
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