I'm not saying he's not straight, I'm just saying that just because he's close with someone in college, no matter how close he is with the guy, it doesn't prove romantic feelings and as such, doesn't make the point necessarily that he is bi.
Frank's bi? Cool. I'm just saying the library scene and him keeping a secret service guy close (which I assumed he was doing because he wanted a young SS guy who would come to trust him so he could use him later) didn't really scream homosexuality of any type to me. That's why the scene was so out of left field and made some people do a double take.
Chapter 8 said:"And what about us?"
"Honestly, I haven't really thought about it that much. It's a long time ago."
"We were so close."
"Like brothers."
"More than brothers."
"We were kids, Frank. We messed around a couple of times."
"I was so drawn to you."
"I could always make you laugh."
If you don't see romantic feelings implied there, I don't know what to tell you. Frank is not straight, and also has had romantic feelings for another man before.