If any of you are with someone else then I think its not right to be around together anymore! But if you have a 4 year old together, then I think you should try to make your relationship good and not just leave each other!
if your ex lives with you (i.e sleep in the same bed) but you're not together, is it right for her to sleep around? keep in mind we have a 4 year old together and she lives with me for free because i took her in thinking we could fix our relationship.
Sounds like you are settling for less than you deserve and she has you by the "you knows" ! You seem desperate so she takes advantage. You shouldn't be sleeping in the same bed or under the same roof. You can move or ask her to, but if she's with someone else you HAVE to let her go.