Great threat,
I agree that all parts are exciting, for me, kissing is always a turn on, I love to see my wife passionately getting kissed and returning, I also love the undressing part, where her boy friend takes off her panties and bra...
A close second if not the first is when my wife will catch hold of his cock and slowly guide it inside her either in the missionary position or cow girl position, if it is too tight, she will pull out and put some more lube and then take it in, when she is on top, in the missionary position, she will slowly take the first bit like a third, and then drop on him, pushing it fully inside, wait a few secs before she starts rocking.
The most intense for me was the first time she let me watch and record her with her boyfriend, she had been going out with him for some time, and was comfortable with him.
But with me watching, we were all nervous, and I wanted to see her face so, so she came on her side and her boyfriend took her from the back. It took her a bit of time to cum, but when she sis it was quite intense and loud. A snippet is attached, with her wedding ring showing.