Perhaps one of the less understood issues about twin flames is the phase of sexual cleansing.  Jenna Forrest groups it within the stage of harmonization, but for me, this is a step by itself.

It usually starts at the end of the glow stage, after the rising of the Kundalini energy. You will start to feel the energy of Kundalini when it begins to awaken, but you will identify it, as a sexual energy. Before this energy detonate, you may have had meetings with your twin flame in an etheric level. But at one point you will feel the energy in your physical body. Will be perceived as if the Beloved were there, making love to you, although we can not see him/her.