nothing odd about this whatsoever. Nothing odd about being in touch with ex's and nothing really odd about meeting up with them.
Our ex's are part of our past - they have contributed to what he have become now. They have played important roles in our lives. Let's face it, we don't meet someone we really connect with every day of the year. Why should we chuck someone completely out of our lives just because we are not in love and/or sexually attracted to them any more?
Sounds like this was a long relationship and, in many ways, I would find that less threatening than if he was introducing you to someone he had a torrid month long fling with. Ten years is a long time, you become someone's friend in that time (and probably stop having sex!!). Life's too short to chuck those friendships away.
The only caveat is if the ex behaved badly/cheated/was abusive or if it ended badly/messily. But if it didn't, if it really was just the end of the road after a long relationship, you have nothing to be uncomfortable about, especially as it will be the four of you.
As for imagining them sleeping together, I cannot remember sex with any of my olders ex's so I cannot for the life of me know how my DW could imagine it!!
You may even be surprised and get on really well with her.
Bottom line is she clearly still has some importance for your DH - and he is doing nothing wrong by maintaining that. If she is still in some ways important to him, best it's all open, that you meet her and that everyone can see clearly where their roles lie.
I promise it will be nowhere near as bad as you are fearing! And remember, you are in pole position, in "possession" of your husband!! This is clearly not one of the many cases we see on here where someone bumps into an ex and there is a clap of thunder.
Don't give DH a hard time, he is being open and honest with you and deserves recognition for that...
[from a DaddyMumsnetter!]