Sorry to see you here however at least this is the right place for talking to a lot of very smart people. Helped me a lot.
I see a few issues but lets look at 3 of the main ones
1 the affair and no contact ( assuming this is correct)
2 the length of the affair is in question - if true means honesty has not been total from WH
3 he was two timing you before you married in high school with the person who has turned out to be the OW ,,,, and maybe some others as well during this time.
Lets talk about the 3rd issue first
As I am assuming this was in fact during your high school years and this was before he committed as an adult to you in marriage & perhaps it should be placed in that context. Yes its hurtful but the words he wrote to her at that time should perhaps not be too much taken to heart. This was the past before your marriage. Let those letters rest in the past. Frankly I suspect he used whatever excuse he could to dump the then high school OW. If there were others he did the same thing. Not particularly very nice however not unknown by young men or women during these years. The concern is that his affair was with the grown up version of the teen OW ... the same person and this raises doubt.
The length of the affair IS a really important issue as it goes to the honesty of the apparent recovery between you over the last 10 years. If he lied about this has he lied about more? Perhaps .... he may also have decided to try and reduce his crappy act of adultery by saying it was 1 year and not 2 or whatever... sadly not unknown from a WS. However it raises concern that he does NOT get it fully. You need honesty to let this pain go from your life... as much as it ever does. You need honesty to recover the M. If he's not willing to be honest then its natural that you question his real commitment to the M because he obviously is not being honest.
finally no contact
From what info you have provided it SEEMS there is no contact except maybe at OC exchange time. I cannot tell one way or the other if there is more. If he doesn't disappear... if he's no longer than you would take to drop OC back at his bio mums ..... if all of it ads up the right way ....then perhaps there is no contact that can be of concern ....... HOWEVER trust but verify is a very sound thing to do in this circumstance. IS he open about his whereabouts? does he let you know where he is? can you contact at any time ????
These things he should be absolutely open with you. He should be WORKING on not just your needs but on ensuring you feel safe in the M he damaged. And he should be quite willing to do so without resentment ... eager in fact.
In short ... I'm wordy too
... you should talk to him about this apparent dishonest story of a 1 year affair and letters which indicate it was 2 years or whatever. If he gets angry its a good sign he's been caught out ... maybe more ???? if he's upset and remorseful then maybe just maybe he was stupid and fearful of the consequences at the time. ,..... you leaving him etc.
BUT as long as dishonesty is in the m you will always doubt ... that cannot but hurt the M
Use the Harleys if you need to but get this out in the open ..... then you can deal with the outstanding issues or problems.
all the best