I find it interesting that, after an hour, she had reason to believe that she could reach SM at that pay phone. That, combined with the short tearful call to her friend, makes me suspect that she was waiting for SM to call her back.
In other words, after the first call, SM may have said that he was going back to the house for a few things ...I will call you back and you can pick me up. She made that quick distressed call to her friend...then waited to hear from him again. After an hour, she tries the phone booth. Increasingly worried, she takes the risk to repeatedly call his cell. Finally he answers. And she leaves for the Landing.
IMO There are only two reasons to call that phone booth an hour later in the middle of the night: one, if they had used it as a point of contact with each other since TM took his phone...or if he told her to wait for another call. After an hour, she is nervous and tries to call him.
Whatever he told her, in addition to leaving his wife, etc....had some kind of urgency about it that caused a fearful Heather to take the risk to call his cell. That is interesting too.
One question for those of you who have read Heather's social media postings from that night (I have not)...if SM and TM had had a huge blowup that night...and TM was already "stalking" Heather online....after SM left the house, wouldn't it be likely that TM went on Heathers Tumblr etc to see what she could find? Would Heathers postings, even if they were posted BEFORE she knew SM had left...have added to TM's rage?
I am not asking for details if not allowed on this thread...just opinions on how TM might have reacted to them. Please delete, Mods, if question is inappropriate.