As I wrote in yesterday's column, semen has no toxic properties whatever. No matter how much semen is introduced into your body, by whatever route (vagina, mouth, anus), you are unlikely to experience any ill effect (unless a stray hair makes you nauseous). It isn't even fattening.
You are only at risk if your boyfriend has a sexually transmitted disease (STD), AIDs, Hepatitus, non-specific urethritis or other urinary tract infection, or other contagious diseases. Herpes and crabs too will spoil your fun. But if you know for a fact that your partner is disease-free, there is no reason why you can't treat him like the soda fountain he's apparently become to you.