Best Friends Turn To Lovers

My Name is Jade. I have a Bestfriendd. His name is Brian. We've been friends since like forever. We do and did everything together. We are insteprable. Just a few ago my best friend .. He told me hes In-love with me. Now I'm confused. I love him but do I like Brian in that way? Dating ur bestfriend? Is that even allowed to happen. That's not in the rule book. His jealous ex Jacqui getting incolved