It is impossible to know if your boyfriend ejaculated inside your vagina, or not, during drunken sex. You can take a home pregnancy test, however, to know for sure. Additionally, you may consider taking tests to identify possible sexually transmitted diseases (STDs). If you experienced a black out during drinking (temporary loss of memory or consciousness), you might also want to monitor the number of times that this occurs. Frequent black outs may indicate early stages of alcoholism.