You're not a selfish cow.
Your partner needs to work on his jealousy issues. And if he wants sex with another woman, he should get his own damn woman and not assume he is welcome (by you OR her) to glom onto yours.
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):
my bf: Ginger, 61, married to:
Robin, 60 (mono)
and dating (NRE): Carla and David, married couple, early 40s