The text messages aren't worth squat really. You tell your side, he tells his, and the judge determines if he is enough at fault to warrant paying for the repairs. If you took his property and refused to give it back and he claims he was just trying retrieve his property, it is possible the judge will not hold him responsible. Using his phone to send a text was inappropriate and juvenile. By all means, break up with the guy but sending a text to the other woman, which I am going to assume was not just a, "Hello, have a nice day", and taking the phone were uncalled for. It is anyone's guess what a judge will do in a case where both parties behaved badly. I do suggest being honest at least. No judge is going to buy that you simply forgot you sent the text and kept his phone from him and only realized it was still in your hand when the police showed up. Claiming so just increases the odds he will prevail.
In the messages he is acknowledging my truck os broken and trying to figure out a way to get it covered...by himself. Seems that should definitely count for something. Why would someone offer to cover or have something he/she did not damage fixed?