Why does he do this help?

i was with a guy a year and a half who had a reputation as a player,he always had more than one woman on the go and went back and forth between them all mother of his kid incuded.so he and i split,but he always called me saying i was the only one he loved.he is seeing someone but wanted to meet me told me he would duump her,i said no.now they are back all cosy,but he rang me up wen she was there saying i was trying to split them up and it wouldnt work.why is this?