I agree with Annie you really should look into therapy to help you control this...you do not deserve to be stuck with this kind of crippling anxiety all the time.
and the truth is, if he WAS leaving semen all over the house (highly unlikely), it would almost certainly be dead by the time you were exposed to it...but I really don't think you need to worry about sperm being everywhere. Men don't just (sorry for the gross image here) spew it randomly all over the place, and most men don't get it on their hands and go on a touching spree...think of it this way, when you pee and reach for toilet paper, say you realize that you didn't get enough to get thoroughly dry, so you reach for more..do you cover the whole roll in pee from your hands? most likely the answer is no..because you're careful about how your hand is exposed to the pee and you're careful about how you grab the TP even if you do get a little bit of pee on your hand..I would imagine the same applies to a man and semen. and as for the bath/toilet, very unlikely, but carry a pack of clorox wipes and use them on the surfaces before you use them if you're that worried.
in the meantime...research therapy options for yourself, you really should get some help because your anxiety is over the top and you don't have to live with it that way.
Any chance of getting some therapy? OCD is something you can treat with anti-anxiety meds and talk therapy, and the sooner the better so it doesn't get ingrained.