get out of there. you never loved her in the first place. now she's been porked by a bunch of guys. there's a kid that isn't yours. you will have to support them both entirely, since she'll need to "stay home for the kid." and now you KNOW she is a runner and she doesn't have scruples about who she sleeps with. she'll use you until she finds someone richer, and then she's going to run again, and take child support from YOU while she's at it.
i know it's really scary to face life without that familiarity... but your old life is gone, and getting back with her won't bring it back. you just need some time to process, come to terms with things, and move on. in the meantime, be patient about your new prospects. they will spring up eventually.