How to be there for sister who came out?

Hey everyone. So, for context, I'm a guy in my early 20s who, just last November, made the decision to come back to the Church. I'm also gay, but for a number of reasons, I've decided to remain chaste. Been actually going pretty well, but recently, my 14 year old sister came out to me as bisexual. Days later, she broke up with her bf (who, ironically, was a sweet Catholic boy) and has started a secret relationship with some girl at school. When she came out to me, I didn't really know what to say. I wasn't exactly..overjoyed, of course. But I also didn't want to say anything hurtful, so i just shared a bit of my story, advised her to be absolutely sure about this, but that I and God (our family is Evangelical) still love her and I'm here for her. While I did mean every word, I'm also struggling. Honestly, despite her enthusiasm, I feel like this is just a phase. Kind of ironic coming from me, but I don't mean it in that way. I have my reasons for thinking why, but too long to get into. Anyways, I can't help but blame myself. And I can't help but be mad at any potential outside influences, as I honestly believe this is what this may be coming from. Anyways, I should probably talk to my priest about this and I most likely will, but how can I be more understanding and supportive during this time? She has already sort of joked that I'm homophobic since my initial reaction, like I said, wasn't entirely overjoyed as she may have wanted. Comments like that hurt me, as I love my sister and want to convey this better, but I also want to be mindful of my own faith. What should I do?