I'm struggling with an issue of licking in-between my sister's toes when she's wearing sexy wedges. Can you give advice?

Question

After quitting this over 7 years ago, I have just started back indulging in licking in-between my sister's toes about a month ago about 2 days per week for 30 minutes each time. Sometimes it's licking in-between her toes and other times, it is sucking her toes and other times, it's kissing her feet or licking the soles of her feet after taking off her 4 or 6 inch wooden or leather wedges or heels.

She helped me overcome a major downfall in my life in April 2012, on the 9th of the month around 4pm to be exact when I was living in Denver, Colorado at the time. It was a totally unrelated issue but the fact of her help drew us together and the bond has crossed boundaries. So far, we haven't done anything involving our sexual body parts but hope it never gets there. What must I do? I am very afraid and I spoke to a member here in private and had to wait 3 hours to ask due to my questions were full.

She intentionally wiggled her foot in my face and taunts me. I told a close friend about this and he said I ought to slap her in the face but that goes against my standards. I have never hit any female and only 2 times ever hit a male. She just has the perfect toe to foot ratio and her toes extend half way past the front of her shoes and it was something I thought I had victory over in June 2010 but crept back in last month, shortly after my 26th birthday. Does spending too much time will my sister cause me to blur the lines and see her as I may see another woman. Please help me. I want to gain full victory over this issue and I'm becoming weak in this area more and more each day. We have Monday and Thursday sessions of this and she is very hard to resist.

Please. Any help will be greatly appreciated. If you believe that this is great, also say so and why. Many just doing this may prevent me from further contact that will scar us both. She's 29, by the way.