A few things to keep in mind:
First, plenty of people were raised with only one good parent, and they turned out fine. Actually, some of the most accomplished people I know had little or no parental guidance. (I grew up in the 80’s.) Be the best parent YOU can be to your kids. Don’t spend so much time worrying about what is or isn’t going on over there.
Next, take the high road – no shit talking about your co-parent. Remember, the way your kids see it is that you bad-mouthing their other parent is you bad-mouthing a part of them. They can’t help that you chose someone with whom to share their DNA.
And hold strong. Be consistent. Set boundaries.