I'm a male and I find that quite weird that he would be chatting up a buddy, whilst looking at pictures of him on a PC and masturbating..and it not be related! If nothing else, ask him for your safety. If he is having sex with men, you need to know. What if hes not using protection? confrontation isnt getting in someones grill and being harsh, just approach him with what you saw and heard and let him explain.