There are (at least) two questions you need to ask yourself before even bringing this up:
have you actually experienced a cuckold relationship? Or is your experience totally just from online porn? I am pretty sure the fantasy is going to be entirely different then actually watching your wife have sex with someone else.
what will your response be if she says no? Are you prepared to take her feelings into account? Again, fantasy vs reality. Certain communities on the Internet make it seem like any woman you suggest this to would jump at the chance but again, reality can be quite different.
It's a hard conversation and it's nice to get a feel for what to say. Maybe I just suck at talking to people, but it's nice to have help sometimes
Not really in a comparable position, but I‘d like to give my two cents on the topic anyway.
My wife and me have been together for about ten years now and open communication always seemed like an integral piece of what made this relationship work. Talking to your partner about what you want, or what you are into, will at least get you on the same page and prevent something slowly cooking up, to blow of the lit later down the line.
On the specific topic, you should know best what to expect from your wife. But maybe you bolster up for an unexpected result. Maybe she’s more into the idea than you expect, and that might hit your ego in an unexpected way. Talking it through is still the best way to go about it, I just like to have several game plans laid out before I tackle potentially difficult topics. Helps me lot in building up the required confidence, even if my wife has the tendency not to fall into any of my preplaned scenarios at all…
I think you can say honestly you find it hot when other guys check her out, or that sometimes you'd think about her with someone as your 'porn' without pushing her to do anything. You cannot push her into being someone else just because you'd find it sexy, but it's not wrong for you to find it sexy.
If she is so wiped out from having the baby she doesn't even have time for sex with YOU, she probably doesn't have the drive for more than one guy! Is it possible you just miss her more active sexuality? It will come back, stay connected and physically touching, do things together.
Honestly, to begin with I'd go to Fetlife or something and ask this to active cuckolds and hot wives. How did people start? What challenges have come up? Do they feel secure in their relationships? Any stories where it went horribly wrong? That kind of thing - anything to get a peek at what this kind of thing is like IRL.
Next, take a hard, unsexy look at your fantasy. What are things that would make this unpleasant for you? Some dudes like being verbally humilated during this stuff - would that be you, or would that hurt? What is your connection with the guy - have y'all had a grownup talk about what everyone wants? Is it just some random guy at the resort? What if you find they are texting after your vacation - is this hot, or traumatic? What if she wants you to do something with the guy (pretty common) - down, or no way? What if she wants to fuck him and you're not present - cool, or no? And so on.
Once you've got this sorted, in terms of approaching the conversation, common pitfalls to be acknowledged, and your hard and soft limits, then talk to your wife. Say you've had this fantasy, and want to know if it's something she would be interested in. What concerns does she have? If she'd otherwise be game, how do you manage those? Talk it out so that a) you both can determine if it's something you want to pursue, and b) in such a way that everyone feels super turned on and excited about the activities, with any risks to folks' feelings controlled for to the best of your ability.
It's not for everyone, but if you think it through, communicate consistently and honestly with your partner, and respect each others limits, it is for some.
Uuhh. Difficult topic. That needs to be something all participating parties like, or it won't work.
I'd bring it up eventually. Say 'wife, I had this fantasy ... would that be something that'd turn you on?' Maybe start slowly with just role-plaing it as a fantasy and see if it goes somewhere.
There are several podcasts on sexual things. Detailing experiences of other people, discussing healthy behaviours... (Maybe you want to visit a Swingers club. I've heard you can have a tour of the place and get an introduction in good establishments. And you can take it slow and aren't forced to participate on the first visit. But that's also something I've only heard about in podcasts and never experienced myself. So there's that. And people recommend not to try things like this to save your marriage. You're bound to fail. So only do it if you're happy together and comfortable.) And I don't know if it's just the flirting for you or the whole thing. I'd say just flirting is more tame. But it also needs to be something the other person would be comfortable to do and get anything out of it.
If you didn't start poly or open, then chances are you won't be open or poly. My advice is to keep this to yourself bud.
If you're really unsure you could wait for the right moment and tell her you had a dream and ask her what she thinks. Or saw some porn or a post somewhere.