Am I dumb: update

Ok over two years ago I met my partner. After dating a couple months he tells me... “just found out my ex is pregnant and saying it’s my baby- she due any day)”

I asked if he knew before we got to together he said no definitely not.

I chose to believe him. Anyhow a month after the baby was born they did a dna test and it wasn’t his. (Thank god).

In the early days/months of dating we discussed past relationships etc and he told me never had he ever felt this way about anyone before blah blah blah. He said the last girl was called *** and she was his first and he really liked her etc but she cheated. 10years later and two months before we got together they started ‘causally dating again’ (hes words).

Anyway I always had in the back of my mind that he really knew about the baby before we dated and that things probably weren’t as casual as he says about the other.

Fast forward to now. We are engaged had a mc recently and are actively trying again. I don’t have any trust issues with him and believe he hasn’t and wouldn’t cheat on me.

For some reason I today decided to look through his instagram account. Don’t no why.

Anyway I found messages from the girl (who said she was pregnant) message was dated a month before we got together.. slagging him off and saying he a shit baby dad etc

This tells me he DID know she was pregnant before we got together.

Also I found messages dated back to about a month before we met from his ex where they are talking about marriage and kids.

Erm I don’t know what to think. Should I say something should I be mad etc

Basically to whole start of our relationship was based on his lies

Should I say something?

I know I shouldn’t have gone through it, I don’t even know why I did.

Advice please

Do I just stopped ttc and finish with him (seems extreme) but does it? I don’t understand why he lied why not just say he knew she was pregnant and why not say he really liked his ex and they were thinking of marriage and kids.

I’m losing my mind over here

UPDATE

So I spoke to him about me reading his messages he was a bit like why do you need to do that, don’t you trust me etc. I reminded him he always said I could if I ever needed to. He said yea I know but why now? what have I done to make you need to check messages etc

Anyway as soon as I mentioned that girls name he absolutely blew up.

“Why are you bring her up again after all this time, you constantly bringing old shit up”

After he calmed his arse down I explained how it made me feel as it clearly shows he knew she was pregnant before we met and I want to try and understand why you lied”

He answered with... “ I never lied to you I told you I found out a couple weeks before we met”

I reminded him that when he first told me he said he found out a couple weeks before. He told me in October we got together August and those messages were dated June.

He then explains he rubbish with dates etc

This is obviously shite.

I’ve left it alone so I can process and evaluate.

Not sure what to do. We are so good together up until this!!!!

My fault for snooping I guess