Oh yeah, Mina did mention your girlfriend...[He's just assuming here, although he briefly wonders if he meant Minako herself. Terra puts his free hand on Ryoji's shoulder, a bit stern, but supportive.]

If you're feeling nervous and uneasy about not having told her...If it bothers you to know that you're keeping this from her, and that you may never be able to tell her...

Is that really a healthy relationship that you want her to be in?
That's why...I feel like I would have to tell her, eventually...
You both should be happy, I don't know if its fair to either party to let a big black cloud loom overhead...You know? [And talking through this makes it easier to look at his own situation objectively.]