I love her and don't know what to do

I have a best friend (we're both girls) and we're very close, we have showers together, we've kissed, hug all the time and tell each other everything. Although I have never come out as being bisexual but I have had a strong feeling I am for 4 years now but still don't think I am for sure. When I'm around her though I'm so in love with her and want to go further with her but I know we're just friends and she doesn't know I feel this way, as it would ruin the friendship. I know I have some sort of feelings for her as I get how I used to with my boyfriend towards her but I don't know if it's just because we're close. I don't know what to do as I don't know if I'm definelty bisexual. Please help