It has been 20 days since i had that event. I havent got any blisters in my mouth region. Is that means i am free from Herpes.
You can't get genital/anal herpes from performing oral sex on someone. Herpes is transmitted skin-to-skin contact (along with heat/friction). For example, you'd have had to have a HSV positive person perform anal sex on you for there to even be a risk of getting it anally/genitally (and, even then a one-time encounter is low risk, even if they HAD herpes). Also, ejaculation has no impact on herpes transmission. Quite honestly, the biggest risk here would be you having oral herpes and transmitting it to your partner by performing oral sex on him.