Hey Rough... Holy HELL have I struggled with this. My sitch got to the point this weekend that the opportunity presented itself for these conversation points to come naturally...
I was able to "set her straight" on her thoughts I might be seeing someone else without having to throw her under the bus for her actions with OM.
I was able to tell her, very explicitly, that I DO care for her, that I DO love her, and that I'll never give up on her, no matter what happens.
In all honesty, I don't think she believed ANY of those things before I explicitly told her. I think she'd convinced herself of many untruths... about me not caring anymore, about me doing exactly what she was doing with OP etc...
I'm not sure that she believed everything I said, but it doesn't really matter, because I was able to say it.
My advice here?
When she comes and drops off the kids, gauge her mood... Feel out the situation. If it feels right, I see nothing wrong with a simple "How's it going?"
Then listen closely. If she responds in a short/quick/dismissive manner, then back off. If she opens up a little, then listen, validate and play it by ear. Show some compassion if it fits, but validation of her feelings IS compassion.
I would highly advice against trying to convince her you're not with OM... You're probably right that she might not believe it... and if it totally comes out of the blue, it'll just seem weird.
IF she's interested... IF she wants to know... You can absolutely bet that she'll bring up the topic at some point... And you need to CAREFULLY consider your response... Balancing out compassion, strength, and honesty is no easy task. Saying you're committed to your marriage without sounding accusatory of her decisions isn't simple.
Personally, I took a pretty strong stance when it came up, but I was sure to balance it out with letting her know that I'm NOT trying to put her down or judge her decisions... I was simply letting her know what MY decision has been.
But in all honesty, I THINK your wife knows you care. And I KNOW EXACTLY how it feels to be unsure of that. So my opinion is this: If it will make you feel better about yourself and your situation without causing damage to what you're doing... Then go for it...
SO LONG AS THE SITUATION DICTATES IT.
Don't force it. Don't shoehorn it in or it will feel forced and you'll be disappointed.
I'm sure others will have their own opinions, but that's my .02.
