I don't think whether you cum or not has much of anything to do with your likelihood of infection. If you were infected and cum inside someone it would increase their chances, but not the other way around.
I'm not a doctor or a real scientist, but as I understand it, if you only top which has much lower odds of HIV infection than bottoms, and you always use a condom, your chances of getting pozzed are extremely low. If you want to further reduce it you could go on PrEP. And even if somehow you were to be infected, it isn't a virtually automatic death sentence within a few years like it once was. With current meds there are lots of people who have been Poz for 30+ years and are still in relatively good health. In fact, for a lot of them it is not likely that they'll ever develop AIDS or die from anything related to HIV. More likely they'll go in their time by one of the more common ways - heart disease, cancer or accidental demise.
Anyway... I wouldn't let it get me too worried.