Hello.
That's a good question--and one that I've been asked many times. As far as I know, the possibility of sperm traveling through many layers of clothes is minimal.
However, why not learn from this? There are many ways to be sexual without exposing yourself and your partner to the risk of pregnancy and/or infection.
If you want to have orgasms with your partner, be sure to use a condom, just in case. there are many brands available. To find out which you like best, I suggest trying several during self-pleasuring. Dr. J