Hello Sir. Thank you for writing for your friend! Well there are two-three issues in the query you asked. Let me explain you about the same. 1. Unprotected intercourse: The first and the foremost thing that you should advice your friend is to not indulge in unprotected intercourse. Condoms or other barrier contraceptives not only help in preventing pregnancy most of the times but also help in protection from sexually transmitted diseases. 2. Regarding possibility of pregnancy, the best way to rule it out is to have a Urine Pregnancy test done. There are various brands of the UPT kit available in the market. Or ask them to visit a gynaecologist to confirm about the same. Though the possibility of a pregnancy is decreased if the girlfriend had a period as usual. 3. Regarding his 'overthinking', I feel the anxiety should be relieved if they get the test done at the earliest. If it remains, I suggest that your friend visit a psychiatrist or a psychologist to check for any neurosis or past history of any pervasive anxiety disorder and take the necessary help. Take care.