There is absolutely no way that you could be pregnant from this encounter. Sperm could not penetrate through the clothing. Even if there were a wet spot on his pants, it would be water from the ejaculate fluid, not from any sperm.
In addition, even dry humping without any clothes does not cause a pregnancy. Sperm actually cannot swim up the vagina to cause a pregnancy. Sperm need to be deposited on the cervix, which occurs during penetration. The sperm actually cannot survive in the pH of the vagina. Only the cervical mucus has a pH in which the sperm can thrive.
If a woman could get pregnant from dry humping, with or without clothes, it would be possible for virgins to get pregnant, and that simply does not happen, at least not without divine intervention.
So, there is no reason for you to be concerned about pregnancy from this encounter. The missed period is most likely a non-specific response to stress. And the negative pregnancy tests also support that you are not pregnant, although I could say that you definitely would not be pregnant even without the pregnancy tests.
If I can provide any clarification, please let me know.