Dirty rat's young lover is pregnant

MY partner is about to become a father - sadly, I'm not the mother.

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He's made a much younger woman pregnant and left me feeling humiliated and ridiculous. This woman is a colleague.

Apparently, they've been having casual sex for over a year in the back of his car and now she’s having his baby. One minute he shrugs his shoulders and says he's sorry, the next he huffs that I’m making too much of a fuss and that “these things happen”.

We don’t have children together, but I have two daughters (17 and 19) from a previous relationship. They're both furious on my behalf.

The new baby is due in November. I know that this mess isn’t the child’s fault, but I can’t help feeling resentful and angry.

The mother and I aren't in contact. His other colleagues tell me she's a decent woman who my partner has lied to and treated appallingly.