What I’m reading is that you had to go fishing for a condom full of sperm. If the fishing expedition resulted in some of that sperm being squeezed out then the chance of pregnancy is real. Try to figure out if you were in the fertile window and consider PlanB if yes.
A condom put on with no slack in the end to hold the cum chances the cum backing up the shaft of the penis and lubricating it enough for the condom to slide off. After the guy cums he maintains his erection only for a short while, which is when someone should reach down and make sure everything comes out together.
He should probably know if he climaxed and ejaculated. We normally remember that. That would be good to know. But the penis can still emit small amounts of sperm. That he wore a condom is good. Unfortunately, coming off during intercourse isn't great but still I'd say a low chance that you got pregnant. But, there is a chance. Remember though, the condom was still inside of you and still acting somewhat like a barrier. You have a couple of options. This really is unlikely you got pregnant but because there is a risk, if it is within 72 hours, you could take plan b. This will prevent pregnancy most likely but does have the down side to the hormones of the pill then being in your body and it would make you probably irregular with your period for up to 3 months (late, early, missed cycle). This isn't that big of a deal but tends to make girls worry. Your other option is to just wait until 2.5 weeks after this happened and take a cheap home test. My guess is it will be negative.