My boyfriend and I were messing around one day and he ejaculated on my hand. I washed my hand and nothing should have been around my genitals until I used the restroom 30 minutes later. But I had already washed my hand and I was also on my period at the time. Could I get pregnant?
I find it curious how people treat sin so casually. Here you are essentially stating that you had your hands on the genitals of a man to whom you are not married. Rather than being sorrowful over you sinful action, you dismiss it as just "messing around." "Were they ashamed when they had committed abomination? No! They were not at all ashamed; nor did they know how to blush. Therefore they shall fall among those who fall; at the time I punish them, they shall be cast down," says the LORD" (Jeremiah 6:15).
Sexual touching outside of marriage is a form of fornication. Just like the warning against the man committing adultery, "Whoever touches her shall not be innocent" (Proverbs 6:29), so it is with you in your fornication. You are an innocent.
While you managed this time to keep his semen from your genitals, there is no guarantee that you will be as successful in the future. People who are sexually aroused do not think clearly or rationally. As with most sins, you'll convince yourself that nothing bad happened the last time so there will be no harm going a bit further next time. Eventually you'll have an "accident," but it won't really be an accident. You will have just gone further than you intended.
I can't make up my mind if I feel sorrier for two people ruining their future over momentary pleasure or the child who will face a broken home because his parents have no self-control. "For this is the will of God, your sanctification: that you should abstain from sexual immorality; that each of you should know how to possess his own vessel in sanctification and honor, not in passion of lust, like the Gentiles who do not know God" (I Thessalonians 4:3-5).
Of course pregnancy isn't the only thing you are risking. Sexually transmitted diseases don't require intercourse to be spread. For example, HPV can easily be spread via hand contact.