Yeah my guess is there is someone else. You've only been married 4 years and have a young child so it's very uncommon for her to just walk away.
I think your last paragraph is perfect and dead on. Don't hang your hat on her maybe changing her mind down the road. That's typical script saying you're plan B.
Lastly, you need to work on validation. The purpose of validation is to let her know you understand how she feels without judgement. It is not to make her feel bad or guilty.
You will survive and things will get better my man.
