I totally understand how you feel OP and I would feel the same thinking of a 16 year old but for context I am 35 (you mention you are younger) and this was incredibly common when I was a teenager. Not saying it was ideal but times have changed.
I had a lot of interest from older guys including in particular a 23 year old at 16 (no sex as I actually had a boyfriend, although that relationship was problematic) but we really got on and it could have developed. He did definitely question the age difference though.
I dunno, I would expect some reflection from a late 30s guy on this not being a nice thing to have happened to a 16 year old but with differences in maturity, maybe he saw them as equals, that's how the 23 year old I knew saw it, anyway...
For me to look past this, seeing as it has been a good 2 year relationship, I would need a conversation about exactly how he saw the experience. If he said for instance, they met socially or at work, got on and he considered the age difference but she was a very mature and intelligent girl and the pregnancy happened despite precautions then that would be different from say, him making a habit of going out with much younger girls because he had no success with other 21 year olds.
I suppose Im saying that in my opinion, just because that's how it was back then, doesn't mean that he was either 100% in the right, or necessarily a predatory pervert. I think the social changes just mean this might be a bit of a grey area whereas now I think it would be more unusual, which I think is good. Girls that age are so vulnerable.
If you are put off irredeemably then it is entirely your right to end the relationship. As I say, just giving you a bit of insight into how it was then. Not condemning or condoning anyone.