I suspect this girl is not really my fiance’s niece. Should I demand the truth?

DEAR ABBY: My fiance and I have been together nine years. During that time, we have had our ups and downs.

Eight years ago, after a year of dating, we decided to move in together. The following year we got into a big argument because his ex-girlfriend was sticking her nose into our household. (She was also dating his brother.) He moved out that night.

We were able to repair our relationship and decided to live separately for a while.

A month and a half after he moved, I found out his ex was pregnant. Her due date was nine months from when he moved out. He swears it’s not his child and that it’s his brother’s. I have tried to let it go because I can’t accuse him of lying just because of the timing of her pregnancy.

We were engaged once before, and I called it off because of this. He proposed to me again two years ago, and our wedding date is set for next year. I don’t want to call it off again, although this is still bothering me.

He knows I was hurt by an ex-boyfriend who cheated on me in the past, and I think he knows if I find out the truth, I will leave him.

He treats his ex’s child like she’s his own, not a niece. He picks her up and takes her out for dinner and to the park and other stuff he doesn’t do for his other nieces or nephews. Should I let it go, or trust my gut?

— SECRET OR NOT IN NEW YORK