Wot to do about my cheating boyfriend who got another girl pregnant?

i have been with my boyfriend (ex now) for 8 years, and the last 15 months being paying for everything as he was unemployed, last week his bit on the side of TWO YEARS turns up at our house...who i didnt know about with their 8 month old daughter, im absolutely devastated, apparantly all his mates knew about her but she didnt kno about me either and has been on and off with her for 2 years as he told her to get an abortion but she wudnt. They got back with eachother 5 months ago. I want legal revenge on this guy but wana kno of some success stories please! He is completely denying it all by the way but there is no doubt that baby is his, he is a compulsive liar!