@sullyfish6,
At 15 most kids are able to judge the behaviour of other people, their parents included. They may have a soft spot, or a blind side for one parent - they may even trustingly believe one parent over the other...but they can still judge behaviour as they see it.
...in other words, if you husband is feeding your son lie upon lie about you, and those lies don't match up with your behaviour, then eventually he will start questioning his fathers motives. However, if your behaviour matches up to his fathers lies...