i have been fantasy about wife having sex by another guy or even into gang bang (mmmf). I told her about my fantasy but she is lk ok with it. She even get more horny when we chat about this topic. Should i actually go with it or just keep it as fantasy?
Just because you have shared the fantasy with her, and she liked it, doesn't mean SHE wants to do it for real. It just means she likes the fantasy.
Certainly if you DO go ahead with anything, you need to make sure she is aware of any plans and is willing 100%.
Also, situations like that can easily go bad, not just as the others were saying - because she may want it more often - but the men you invite may get rough, or if she changes her mind, they not like it, and force her...!