My son asked me, "How can you trust someone you love when you find out they have been lieing to you". This person is his ex girlfriend who moved out 1 week ago and he found out through a text that she has been cheating on him. She is the mother of his 8 month old child.

Trusting a liar is almost an oxymoron. Just because she is the mother doesn't mean he can't be a great father.

"trusting a liar" that line in itself already contradicts.

How can you trust someone who doesn't tell the trust? You can't.

You trust that they will lie all the time, so you just keep in mind to believe the opposite.

Trust is earned and if it is lost then much work has to happen before it is regained.

It's almost like trying to trust a dog that has bitten you.