My first thinking on reading the last few post is that if she's willing to dish her number out and have flirty text with you the boyfriend is irrelevant. I think she would have put out depending on how much time you invested in her! The question is... Is she worth the time it would take to get into her pants? If she can give her number out and flirt and go on a date with you she obviously doesn't care about her boyfriend to much! She's just testing you to see what you intentions really are. I don't think there is any easy way around this other than cut the tie if she's not worth the hassle. I know you are wasting you time by going on the date with her but you will learn something everytime this happens.