Welcome back, OP.
I don't think you are crazy. I feel sorry for how you feel (and don't mean that in a patronising way, it must be horrible).
There are different views on here. I am very much in favour of friendships outside marriage - of all kinds, and with people of both sexes. No truck with outside sexual relationships but I also think flirting, if that's all it is, is pretty harmless. I find the idea that life becomes so limited after marriage that things that don't constitute unfaithfulness are off limits simply because it's assumed that is what they will turn into, oppressive and joyless.
I don't just want to invite her so I can spy on their relationship
This is good, because it will end in tears if you are, it's better that you are keeping an open mind.
MN is great and there is a lot of support for other women (support that I have been very grateful for). But having been on here for many years, in different incarnations at different stages in my life, I have come to the conclusion that there is some bias.
Specifically, there is a lot of suspicion of men, an assumption among many that they are all lying, cheating bastards, opportunists who will have affairs given the chance. That bias is because MN is where lots of people turn when their relationships go very wrong. 'Relationships' is a sounding board for a population that has a more than normal percentage who are victims of trainwreck relationships.
There are people on here whose own bitter experience is projected onto others. Who were cheated on, and assume all men are cheats. Who will tell you horror stories they mean to be salutary. Beware of letting it cloud your views.
I hope that you will give this woman a chance and keep an open mind. I do think it's unreasonable of you to call her the 'OW' with no evidence, though this is obviously what she is in your head.
With luck, meeting as families will normalise everything. If you and your dh have a good relationship and things in common (and it sounds like you do) and he likes her a lot, then there is every chance that you will like her also and find you have things in common. And it will be a new connection that makes everyone happy.
Apart from anything else, your husband sounds like too nice a guy to invite another man into his house who he is cuckolding, or intending to.
He may have a crush on this woman, but that can be harmless as well. I get 'crushes' on both men and women, but they are not sexual, it is more to do with the excitement of connecting with a new, interesting person. And that shouldn't necessarily be outlawed by marriage. Just because you have these jealous feelings doesn't itself validate them, though many on here would say it does.
He's not hiding anything from you as far as I can see. Which makes me think: 'not guilty'.