Prior to my divorce from my ex-wife we were legally separated and during that process we negotiated a property settlement agreement which included alimony and child support. That was in Virginia and state laws differ but my first question would be; does he have a legal separation/property settlement agreement? If the answer is yes the only remaining expense would be the cost of the divorce.
"He gets nervous and hides the phone?" Frida, this doesn't pass my sniff test. Although I carry a cell phone there are times I turn the darn thing off. One of these times is when "the time is right" or whatever phrase those ED commercials use, AND I'M MARRIED. Now I'll retract this if he's a doctor, fireman, policeman or has any kind of job requiring him to be on call but I'm guessing this is not the case. There have been several "special women" in my life and I don't recall a single time I wished the phone would ring. Having that cell on while in her presence is a really bad sign and I don't care who's calling.
He's got an amicable relationship with his ex-wife but she's having an affair which he's aware of and he's still "legally married". I'm sorry Frida, I have a bad habit of reading what folks write and I can't get there from here.
His ex knows his daily schedule because his adult children keep her informed. Does he have one of those old fashioned cell phone where you have to know the location of a person before you can send them a text message.
He lives an hour away and she sees him only on weekends. Hmmmmm, is it possible that he's still with his wife and when he's with her and his cell rings he gets all nervous and etc., etc. If you friend does not have independant verification of his maritial status, it's possible he's having his cake during the week and eating it on weekends. (Sorry Frida, couldn't resist the pun).
One last thing and I'll give someone else a chance, he's been thru a difficult divorce and has a real fear of commiting again and is using the cell, text as an excuse to create just enough mistrust in her mind to maintain this relationship as is. This I can relate to. When meeting my now second wife half of me said "oh boy, this is the girl for me" while the other half said, "be afraid, be very afraid". That's a natural emotion but within a year I had eliminated the afraid part .
Frida, based on what you've written I'd suggest your friend protect herself from heartbreak by giving this guy the gate.