Thats why I advise people to take time to heal and recuperate by following the “1/2 Rule”: Divide the length of your last relationship by two. That is how long you should wait before dating someone again seriously. So, if you dated someone for two years, you should wait a year before settling down again.

Can I keep my child away from his fathers girlfriend?

You may or may not be able to stop the other parents significant other from being around your child. In general, you do not have the power to dictate which adults are around your child when they are with the other parent. When you have your child, you can decide who is present.