When I think of sexual stuff or look at women with sexual intentions her body figure, I immediately get a erection with leakage of semen in my pants!?

Normal. That is not unusual with sexual arousal. It is called pre-ejaculate or pre-come, and is known to contain spermatozoa.
Normal. It is normal to get an erection with arrousal. In the beginning of this process there is often a small amount of semen that is expressed.