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It doesn't sound super likely that she is pregnant if most of the time you don't penetrate and when you do, you use a condom. I wouldn't necessarily trust wiping off your penis in place of a condom, but if that's the only time it's happened it's not very likely, especially if you weren't penetrating for that long. Do you mean you tested 8 and 10 days after sex, or after her missed period? If it was before her missed period it's okay to maybe test one more time, but it doesn't sound very likely. Stress can do a number on someone's periods including being late or missing them entirely. Other factors can be a change in weight/diet/exercise routines or if she has been sick recently. If her period doesn't end up coming at all or this becomes a recurring issue it may be a good idea to see a doctor to make sure there isn't any sort of medical reason why she misses periods. I'd also consider birth control if at all possible so there's even less of a chance.