Gosh, I'll be honest. Are you just looking for a reason to end this? I have never examined my husbands underwear -- pants in this case, so closely. I would certainly need more facts than that to accuse him of cheating. Tell him to do his own laundry. You can chat about your feelings on porn - but you really can't tell someone they can not madturbate. If you hate porn, share that with him and see if he can respect that. How is your sex life and relationship with him?
You are saying you feel he had sex but some of the ejaculate was not inside the woman's body and got right on his pants? What would has pants be doing up that high if he was having sex? You might need to think this through.
If he was ejaculating without a partner, it seems like he would probably have his fly down and his pants off his working parts.
You say "it's hell to wash off." Ejaculate (and for that matter, female secretions) are water soluble and come right off in the wash.
Think it over again.
Gives me a new idea of the guys who do valet parking where I sometimes go to dinner.
Yeah, no semen comes out in the wash, so it's NOT THAT. However, it doesn't sound like you are particularly happy in this relationship. You've mentioned that you don't like the same things when it comes to sex, and now it's not happening. That can be an issue that you can work on with a therapist. You and he never see each other awake, can be helped with him maybe going to college or university. He can get student loans for that and ask for a living allowance so you can afford for him to quit his 3rd shift work. If you or he doesn't think the relationship is worth saving in these two suggestions, that would be enough for me to call it quits, especially if you've been together only 3 years. Believe it or not, you'll get over it and find someone more suitable in bed and out of bed. and so may he. Friends help but complaining to friends only goes so far. . I hope you have friends to talk to, but action and commitment to the relationship on both your parts are the only things that will make a change you can be happy with.