NC'd for this but regular - yoni massage, T-rex arms, supersoaker etc.
DH and I have been married for 9 years with one DC (10). DS was the result of what was meant to be a ONS but when I found out I was pregnant and told DH we decided to make a go of it. Bearing in mind the circumstances, things have worked out well. He’s a great husband and father.
There is only one thing that nags at me. He has a female friend that he’s known the whole time we’ve been together. He met her about a year before he met me. I found out from one of his other friends, his best man actually, that they (DH and female friend) really fancied each other but at the time they met she was with someone else. Between our 'ONS' and me finding out I was pregnant they were apparently on the verge of getting together as she’d split up with her previous BF but when I told DH I was pregnant he ‘did the right thing’ as his best man put it.
She met and moved in with someone else a few years ago. DH has stayed in touch with her throughout our marriage. They don’t see each other very often as we don’t live close to her and tbh the contact is just emails every couple of months or so. I confess I’ve snooped 
but mostly been reassured as the emails seemed to be just general chatty catch-ups. Very occasionally DH paid her a compliment but there was nothing to suggest anything untoward. Even so I can never shake off the nagging thought that she’s different to his other friends or more special to DH in some way.
Sometime before Christmas the emails became a bit more frequent and personal as her relationship was obviously in trouble. She seemed to be pouring her heart out about it to DH and he was very supportive and used very warm complimentary language towards her. He rarely talks about her to me so ‘officially’ I didn’t know anything about this IYSWIM.
DH told me earlier, in a ‘hey you’ll never guess’ casual conversation, that she is moving to the city where we live in a few weeks as she has changed jobs or is being relocated or something like that. I asked about her DP and he said they’d recently split up. We live in a small city, it’s not like London where there could still be 30/40 miles between us. He is already talking about helping her to find somewhere to live so she doesn’t end up in a ‘dodgy’ area and I’m half-expecting him to find her a house round the corner or something.
I'm ashamed to admit that after he told me I looked at his emails again. There was one from early March where she mentions the possibility of a job here but then nothing more. There is nothing confirming that she is definitely moving so for him to know this he must have either spoken to her, or deleted the email (why delete that one and leave the older one?) or has switched to another email address I don't know about.
AIBU to feel uncomfortable about this? I feel like there’s unfinished business between them, that the recent emails have brought them closer together and rightly or wrongly I hate the idea of her being on the doorstep and them being able to have a much closer friendship IRL. I felt ‘safer’ when she was 150 miles away IYSWIM. Now I'm also worried that he's having even more secret contact with her. :(