Hello!
Wow, my first post, what a day this is!
I'd recommend not worrying about the boyfriend thing at all. It's only a big deal if you make it a big deal.
Look at it this way, if she's having more fun with you than him... you got her.
One thing you might want to look at is how you found out she has a boyfriend. If someone else told you and she hasn't mentioned it, it's a huge IOI. On the flipside a lot of HBs use the 'I have a boyfriend' thing to disqualify guys very quickly. Either way, it does sound like she's into you.
I'd recommend putting her on a point system, with the promise of some hardcore palm reading if she can get to 20 points.
Have her jumping through hoops for a few days to earn points... give them and take them away etc... and when she's on 15 say, 'hey, you wanna know how to get the last 5?'
Then suggest that if she buys you lunch/drink (your call) then she'll get 5 points and you can do the palm reading at the same time as the meeting.
If she's into you and you play it right, she WONT mention her boyfriend again. The only time she would, if things went perfectly, would be right before sex... and guess what, same as before, it's only a big deal if you make it so! She'll say it before sex because it removes some of her guilt for doing it... if she can tell you and you're ok with it then she wont feel so bad... in her head anyway!
Oh a quick game I like to play:
PUA: Hey, I bet I can read your mind
HER: No way!
PUA: I can, I bet you can think of any number between 1 and 100 and I'll be able to guess what it is first time...
HER: Yeah right!
PUA: Ok, I'll get you a drink if I get it wrong, but you have to pay if I get it right first time.
HER: Deal!
PUA: So think of a number between 1 and 100, remember I can only accept your first answer so don't change your mind.
<wait a few seconds>
PUA: Ok are you thinking of one now?
HER: Yep!
PUA: Great I knew you were thinking of 1

HER: Wait I thought you meant....
PUA: Remember the rules! I can only accept your FIRST answer!
HER: Lets go to bed! (perhaps not but you'll get the drink!)
Hope that helps,
Ocean