16 is a good age to have a special friend. He is old enough to know what you expect of him. He knows how to say no and stand up for himself. He also knows if he has questions he can ask you. Better now than away at college.
"Going out" sometimes means going to your home and watching videos or playing video games, board games. Maybe eating dinner with the family. Your son going to her home to visit.
Maybe going out to a movie, to have pizza. Going to a school dance, carnival, festivals. Concerts. Going to Church sponsored events. Meeting up at Church and sitting together,.
And yes, lots of texting and talking on the phone..
When you were a teen didn't you spend hours on the phone with your friends? boys and girls?
Explain that if they are going to a movie or to a meal to discuss openly with her transportation, whether he is going to pay or they are going to go "Dutch (they each pay their own way.) Make sure you are clear on a curfew for EACH event.
I liked to tell our daughter. "I know you will make good choices. I trust you."
"Call any time you feel uncomfortable or do not feel like going along with other peoples poor choices and I promise not to ask any questions..."
"You can speak about anything with me."
Hang in there mom, he is growing up. It is going to be ok. Just keep an open conversation with him about his future plans. And his beliefs.