haha reminds me of this thing i had with a friends ex once. Every time we were at the same party or something we would end up hooking up, even though she always resisted a bit at first and it was a bit of a secret because we didnt want our friend to find out
We were pretty normal with each other, just like normal friends, but as soon as we were drinking and there was an opportunity to slip away, sure enough one of us would crack onto the other and they would give in.
I say just roll with it, dont make it a relationship, but just realize you are attracted and enjoy it for a while.