1st off you should take care of your child n who cares if it's his, the baby needs you more than anything don't let your emotion take over the best in you, the baby does not need a father figure like that he/she needs some one responsible.
2ndly you guys were together and had an open relationship?? o my gosh... for sure one of you would found someone else, guys are greedy pigss, unfaithful when they have the chance, plus they love to LIE it's in their nature. for sure he left u for that girl n that girl ur friend is a horn dog not a friend material. i hated when men are not responsible for they're actions.
you should jsut move on i know that it's hard but think about do u want a losss er who can not stand up for his words? he already moved on with his life and forsure that girl that he's with is not as great as your are, there's soooo many guys out there.
you should work out n stay in SHAPE, make your self feel more happy and healthier. trust me u will feel more attractive, make your self more attractive, change hair style, become more mature like an adult i find that more attractive. seriously when your change yourself and move on with your life maybe oneday that lying horny immature boy will want to get back with you but when it happens u have to be STRONG and learn to say NO.
you better without him, he will always cheat n u don't want to waste you tears for losers like that, okie dokie