Question on Return Offers

Hi all,

I am a Sophmore intern at a BB, and I have already accepted an offer for next year at PE firm. I don't want to get a step ahead of myself since I don't have a return offer yet, but I have been asked multiple times if I see myself working for the firm in the future. I apologize if this sounds selfish, but I have said "yes" and I have been working hard to secure a return offer so it looks good on the resume.

What's the best way to inform my firm after my internship that I will not be returning back without burning any bridges?

Thanks,