crushing on my bff

okay so i’m in a relationship with the same guy for about 17 months. and my best friend and i (female) have a weird history but we reconnected about a year ago and lately i’ve been thinking about my friend romantically but i am in love with my boyfriend but i’m just sort of confused because these feelings haven’t shown up in like 3 years towards her. and now i’m wondering what i should do. she and i are each other’s only friends because we recently just let go of one of our other friends so it’s just been me and her lately and then the feelings started popping up. any advice?