Should I Tell Him The Truth? Or Do I Let Him Think That The Pregnancy Was An Accident?

I am 18 years old. Last Thursday night me, my best friend (Rachel, age 18), a co-worker of mine (Marcus, age 25), and my co-worker's friend (John, age 30) got together to have a few drinks at John's house. It had been planned in advance that me, my friend, and my co-worker would leave the house at around 2 AM, since my best friend's mom wouldn't let her stay over night since she had to pack the next day to go back to college. Well I'm not one that can take several shots of alcohol and I went past my better judgment and did so anyways. Well at 2 AM I was in no condition to be riding in a car let alone leave the house and so my co-worker drove my best friend home and then he went home himself. John allowed for me to stay at his place to get better. John had been routinely checking in on me to see if I was alright, it took me until about 4AM to get better and then I went to find John. He had fallen asleep in the living room and so I woke him up to let him know that I was all better. We stayed awake watching TV, I fell asleep again and awoke at 7 AM. I asked him if he wanted to head upstairs to go to sleep (with the full intention of actually sleeping). Well, one thing led to another and John and I had . I am not on birth control and so what I usually do if I am in the middle of having unprotected is that halfway through the I tell the guy that I am not on birth control and we figure things out from there. Well, John didn't last as long as I had anticipated and before I could tell him that I wasn't on birth control it was too late. I haven't said anything to John and I never told him that I was/wasn't on birth control. I won't know if I am pregnant until later on but I just want advice on what I should do if I become pregnant. Should I tell him that I wasn't on birth control and so the pregnancy is mainly my fault? Or should I play dumb, let him think that I was on birth control (which is probably what he umes since I didn't say anything), and act as surprised as he is if I become pregnant? He already has a 10 year old son of his own and the reason for this is because the mother (John isn't with her) lied about her birth control. With all luck I won't become pregnant, but I am 18 so im pretty fertile and he's 30 and he has already gotten someone pregnant before so I'm sure that he could do it again. I barely know the guy, in fact Thursday night was the second time that I had seen him, the first time he had gotten so drunk that he had to be carried upstairs by one of his buddies and he ped out in the bathroom. We hung out all of Friday and I got to meet his son and we all had a great time but I still barely know him which is where the concern is. Any advice?