Does thinking about sexual stuffs or doing frequent erection with leakage of semen when arouse like frequently in a day cause acne, pimple in 18yr male?

No: Acne is caused by changes in the hormones during adolescence. It's also aggravated by bacteria on the skin. Frequent ejaculation and erection does not affect acne pimples.

It does not: You're a grown man now and you need to be discerning. "Erection with leakage of semen daily?" Come on. At your age, you should have at least a dozen good erections every day, and almost all your unmarried male friends are masturbating several times a week. It's good for you. This does not cause acne, and even if it did, all acne is manageable. Ask your doctor.