Invited in to have sex with her husband

I am the office wife of a married man. His wife knows me and she and I have had lunch more than once. She asked me if I had gotten intimate with her husband, and I replied no. She wanted me to know that if it was me she would be ok with it, sometimes a man needs a young fertile girl. 

When she asked me if I wanted to go to the beach with them I declined. I was afraid that she was going to insist on me becoming intimate with him.  But it was when he told me that he just didn't want to wake up anymore with me not being there that I relented. His wife has to supervise. Having him make love to me with her watching wasn't exactly what I expected. I slept with him with his arm around me and she slept beside us. 

I'm now family, we are his women. Whenever he has sex with me it is with her present.  She wants to watch and masturbate. She usually gives him oral after he's had sex with me. To date he hasn't had sex with her with me present. 

The obvious question is how does this affect me. I'm 28 and they are in their late forties. 

Guessing your not a virgin so you must have fancied him to fuck him maybe she turns you on try fingering her and see what happens she may want to taste your pussy. I would