Evidence derived from social media, text messages or email can be admitted as evidence as long as it is relevant and there is evidence showing it is authentic.
That means your Facebook posts, Instagram rants, tweets and other electronic communications could be fair game to prove things in your divorce or child custody case. They could be used, for example, to show that you seem to have more money than you have claimed when determining your child support obligation. Your ex could use them to show your behaviors and attitudes during your custody case.
Relevance and authenticity
That said, the evidence does need to be relevant to an issue in your case. Not everything that matters to you is relevant to your family court case. Just because you disapprove of something your ex has posted does not make it relevant. Whether it is relevant depends on the situation and the context. Your attorney can help you determine if the evidence is relevant.
The evidence also needs to be authentic, and you must be able to present sufficient evidence that it is. Ideally, the evidence would be time- and date-stamped with contact information clearly visible.
If a judge decides that certain social media evidence is both relevant and authentic, he or she will admit it into the record. This does not mean that the judge will rule in your favor on the overall issue. It simply means that the evidence will be considered when they make their final decision.