Dear Want to Get It Right…
As long as the elements are clear, you’ll get it right. Texts should be distinguishable from the regular narrative, and readers should easily follow which character is texting which line. HOPE AND OTHER PUNCH LINES does those things well:
Me: I have a plan
Jack: You really need to let this go. You sound insane
Importantly, the punctuation in the texts you’ve sampled is not perfect. Jack’s first sentence ends with a period, but his second does not. Me’s only sentence has no period. That’s realistic. Most folks don’t use impeccable punctuation, capitalization, or even grammar in a text. With a commitment to clarity as your guiding light, be a little loose with those elements—as it suits each character’s nature, of course. Lengthy, properly punctuated texts might be perfect for one character, while two-word, unpunctuated replies might suit another. Style your texts to convey the distinct voices and personalities of your characters. Something else to keep in mind: autocorrect is powerful. If you type an abbreviation, autocorrect will likely try to “fix” what it perceives to be a misspelling. Thus, abbreviations used for slang or to indicate quick-texting might feel unrealistic to readers who let autocorrect do its thing in real life. For example, “ur” might correct to “it” when what you wanted was a slangish abbreviation for “you are.” Try this: Enact the texted conversation on your own phone, borrowing a friend’s phone so you can play both parts. See what happens when you type in each character’s texts. When does autocorrect force abbreviations to full words? Would characters be quick-texting at that moment and not want to lose time fighting autocorrect? Would they be texting slowly and carefully at that moment, double-spacing at the end of a line to get autocorrect to add a period and capitalize the next word? The resulting realism is worth the effort. If this is for a manuscript, not a book you’re independently publishing, your format might change when a book designer does their magic with it, in consultation with you and your editor, of course.