The problem with texting as evidence is that the person that wants to use them has to prove that the texts were sent by the person you claim.  That they wrote it.  If some one states that they did not have exclusive use of the phone then that could rebut your claim.  So then you need additional proof.  There are tools used by experts such as Paraben which is an iformation  "collection" tool  but expensive for your purposes. Good luck.