["Someone gave my husband and I tickets to a concert and we can't wait to go, but my sister really loves the band we're seeing so I feel bad going too.", 'Yea that is kind of a weird situation. I am sure she would want you to have a good time though.', "She did say she wanted us to have fun but she's been kind of quiet and evasive since then.  Maybe I'm reading into it."]
I wouldnt let it ruin a good time. Just dont mention it anymore maybe. Im sure you feel a little guilty.
Someone gave my husband and I tickets to a concert and we can't wait to go, but my sister really loves the band we're seeing so I feel bad going too.