You seem to be only asking whether she likes you. What does to like someone mean in the US? - I`m British. I think it`s certain that she either "likes you" or is planning your demise. I can only speak for here, but I`d guess the demise option would be down around one thousand to one, or so. How could she be deliberately spending time with you without first liking you - How would that work? Her boyfriend isn`t present so that route hasn`t been discussed. Out of principal, your aware she is taken,(and I consider a boyfriend to be taken) I`d stop precisely there! Under these circumstances it`s not for you to do/ask anything more beyond your present social circumstances, and she should both understand and respect this/It should work in your favour. I`d leave it at,"pity you`ve got a boyfriend isn`t it"
With a strong instictive mind, a rare commodity, you`d likely know what she feels, and with a weak one you`d miss nearly everything, and take the rest the wrong way. If more than a few people, it`s easier as an on-looker, think that she fancies you, it becomes quite unlikely that she doesn`t; but it`s only reliable if they`re other women. It`s always good to tell girls that their attractive, but that`s entirely different to telling them that you fancy them. To respect her is also to respect her relationships!