Long time watcher, first time poster so sorry if my formats a bit off.
TL;DR at the bottom

Bit of backstory first;
Known this girl (we'll call her Susan) since we were 16, we are both currently 20
Liked her when we went to school together.
I recently got out of a 3 year relationship and was starting to mingle again on insta when Susan messaged me and liked all my photos so I replied and started talking to her.
We spoke non stop for a couple of days and set up a date to catch up.
A day before the date she told me she is dating this guy and didn't say to much else.
I didn't know what to think and my mate adviced me to go on the date anyway and suss it out.
Went out on the date with her,
Picked her up, went out for lunch and had a chat then saw a movie.
I felt like she had given me a few mixed signals and wasn't too sure what her intentions were.

My Intentions were to suss things out and see what the go was with her bf.
We sat down in the movie and halfway through I thought fuck it, I'll just hold her hand and if she pulls away I will know Susan's intentions straight away.
Go to grab her hand 
She places it in mine and holds it for about 2mins before letting go.

After the movie we spoke about it and she told me that in high school she also had a crush on me but she doesn't want to disrespect her bf
2 days later we are still talking and things seem to be okay
She said we can't see each other again for a while though because her bf doesn't want her seeing

TL;DR I went on a date with a chick with a bf and held her hand. Am I the asshole 