Anything is possible, that's the world we live in. I have yet to know of one woman/girl scientifically, medically, personally proven, who got pregnant by fingering. It takes one to penetrate the egg but there are over 200 million running the race against a harsh environment (vagina's pH) and swimming upstream to collide with said egg. In the op's situation, the alleged sperm on the boyfriend's finger would have had to survived being doused in water (twice), perhaps wiggle out from under the fingernails and then find its way to the cervix. If he ejaculated on his hand and then immediately shoved the hand up her vagina, then maybe the chances of becoming pregnant would become slightly higher, but there is a reason why sperm shoots from the penis with such forceand numbers...to adequately meet the small nearly non existent hole of the cervix.
My logic is if you don't know what consequences your actions may have, don't do them and I notice this particular question is asked alot among the youth. Anything is possible, but this is just HIGHLY unlikely.
It IS possible to become pregnant from fingering. The sperm can live up to five days outside the body. BUT if the person has washed with soap and hot water it is unlikely, that is not to say in this case that is true. If he only washed with water, then fingered you, a pregnancy might occur. That is not to say it will, but it is possible.
It takes only one sperm to find its way and it doesn't need copious amount of semen to achieve this. Semen is very good at surviving outside the body.
Depending on your cycle length, day 13 is a bit of a risk.
To reduce the spread of germs and practicing good hygeine, then sure he should wash his hands with soap. I'd be more concerned about the dirt under his nails than from concieving.
I stand by the belief that one cannot get pregnant from a finger. He would have to had squirted his semen directly inside of you or his scooping it in by the bucket full.
If this continues to make you nervous, maybe he should do you first.