She went to see Cid but Seifer was the kind of go-between or contact in the first place. At least that's what I remember.

Here is the relevant dialog about their past relationship:
Rinoa: "I...really liked him. He was always full of confidence, smart... Just by talking to him, I felt like I could take on the world."

Selphie: "Your boyfriend?"

Rinoa: "I don't really know. I... I think it was love. I wonder how he felt...?

Selphie: "Do you still like him?"

Rinoa: "If I didn't, I wouldn't be talking about it. It was last summer... I was 16. Lots of fond memories..."
i believe there is also some optional dialog you can get with a random Forest Owl while you're on their base. It mentions Rinoa being with a guy a lot last summer or whatever. It's been like eight years since I played this game though so I don't recall the exact details.