Im in a relationship, but want someone else?

ive been dating my boyfriend for almost two months and i thought he was the one. but every time i kiss him now, i picture the other guy. ive already kissed my secret lover and im scared. i dont know what to do. my boy friend says he would die without me. and i dont want him to do anything drastic. my secret lover wants to be with me, but also has a significent other (that is pregnant). WHAT DO I DO?!?!!?!?