I can definitely relate with the first part. The first time I was penetrated was from behind with me on all fours on the edge of the bed. When his head had made its way into my tight little ass and then I felt both of his hands firmly gripping my hips as he began working his cock around to open me up to take the whole thing was a definitive moment.My husband said when he felt the guy's head touch his ass and then start to go in, he had an "oh sh!t, it's happening" moment. That point and when he could feel the guy twitching inside him as he was cumming inside were the pivotal moments. I just loved the whole thing. I'm usually the one getting fucked, but not these times. I finally was able to watch and enjoy it.