How do I tell my husband that he’s not the father of our child

We chat very often and one day he suggested we go for a drink. I told my partner I had a meeting. There have been lots of “meetings” since.
We make love in his car every week. I had been starved of love for years. When I started the fling it was just for the sex. I thought about it all day.

Then I fell pregnant. My partner just assumed the child was his and I didn’t want to destroy him by telling him different but I am 100 per cent certain our eight-month-old son is my lover’s child. He knows the baby is his and dotes on him.

We have fallen in love and are now planning on being together. My lover is going to tell his wife soon.

I know it will tear my partner’s heart apart to find out I am in love with another man and want to be with him, and that he will lose his little boy.

I never meant to hurt him but I need to find an easy way of breaking the news