Read this article about the "rights of a secondary." Might be easier to take in than some of the responses here, which come across a bit harsh.
Rules to be cautious about
Both primary partners must be involved in some or all aspects of the secondary relationship
This might be as far reaching as 'you have to date both of us, or if you date one person, both people must be there'. Or it can be more specific such as 'both primary partners must be there if there is any sexual contact'. This suggests that the primary couple is prone to jealousy and insecurity, and I don't think this is the healthiest way to address that. This can be a way of controlling the relationship, and can make it difficult to establish healthy relationships of any depth.
As a secondary you:
ave the right to have a voice in the form my relationship takes. I am a person, with my own needs and my own ideas about what's important in my life; even when I am joining a pre-existing relationship, I have a right to have some say in the time I can spend with my lover and other things about the form and structure of that relationship. If my partners attempt to impose pre-existing agreements about the form, time, or circumstances under which I may spend time with my lover, I have a right to speak up if those agreements do not meet my needs,and I have a right to have my partner and my partner's partner hear me and consider what I say. That doesn't mean they have to do whatever I say, but it does mean that I can and should have a voice.
And so on. More here:
There is no need for you to force yourself to fall in love with, or have sex with, this wife, if it's really only the husband you desire sexually. She does not NEED to be present when you and the h have sex... that is just something she thinks will reduce her jealousy. It won't! It will just be bad sex, if you 2 women are straight. Even if you do get to explore some latent bicuriousity, and have some sexual fun, chances are things will still get ugly rather quickly, if she sees him paying more attention to you than to her, in bed. NRE will do that. We've seen men not able to get it up for their primary when the new lover is right there, all exciting, unmapped territory.
Love withers under constraint; its very essence is liberty. It is compatible neither with envy, jealousy or fear. It is there most pure, perfect and unlimited when its votaries live in confidence, equality and unreserve. -- Shelley
me: Mags, 58, living with:
miss pixi, 37, who is dating (NRE):