Search Results: adding guys on facebook

So I've been dating this guy for about 1 month now
He has been treating me right so far - taking me out to dates often during the week, holding my hand, showing affections in public, etc
We made it official last week
He told me about his past relationships:
- his 1st girlfriend lasted more than 1 year and cheated on him and he said he hasn't talked to her since they broke up 10 months ago
- his 2nd girlfriend lasted few months

So anyway, I was stalking his facebook and i came across a post from last year
It was this girl with his family
I clicked on her profile
And her cover photo is a picture of the guy im dating and her
And then i scrolled down and she's been posting stuff for the guy that im dating
Its saying that she still loves him through their ups and downs
This post was 2 months ago
And posting pictures and videos of them both
But it says on her profile that she's "single"
And it says that they were meeting up on valentines day (which was 3 months ago)

I confronted him about this and he says
"Thats my first girlfriend.. Im telling u the truth.. i haven't seen her since we broke up.. we dnt talk anymore"
But I dont entirely believe this because it doesn't add up
So i told him that im going to message her to find the truth
Its weird that his ex girlfriend still post about him and has a picture of them on her cover photo right?
They dont have each other on facebook though (theyre not facebook friends)

Should I message her?
Or trust him?