Replying to I had sex

So i broke up with my gf like 3 weeks ago and about two weeks ago she got a new bf. This past friday i got really really drunk and aparently had sex with my ex. I wouldnt care but she told him and now he wants to fight me. I had sex with one of his gf's in the past which caused their breakup so he hates me. I honestly could care less because he is a tool but i wanna hear what you guys think i should do. Im on my phone so i cant show a pic of him but it is needed for this thread so i will give a police style mental sketch: about 5'5" lots of acne, long blonde skater hair. Only wears monster clothing, white skinny jeans, osiris shoes, rides a spray painted shitty bmx bike.