Maybe I’m getting a little ahead of myself right now but… if I take a second long-term girlfriend, would it be advisable to introduce the idea of a threesome with my first girl? Or the worst idea ever?
I think this is a terrible idea unless you REALLY know what you are doing - which... no offense, if you did, you wouldn't be asking this question. Putting two GIRLFRIENDS together is generally a bad idea.
Now, if they are two FUCKBUDDIES whom you have not yet had any prolonged relationship with, then pimping them together is a good and easy way to make a threesome happen.
But if there is a strong emotional bond (usually occurs through prolonged relationships - i.e. "girlfriends", then the risk of creating heavy jealousy (like hardcore) and other bad vibes is very likely to occur. Women are competitive and they want to feel exclusive. This is put at risk when you put her with another girlfriend - another girl who you have a deep connection with.
That all said you still have some viable options:
- Get them to join you to swinger clubs/events
- Get a random girl and invite her to join you and your GF - Either a new fuckbuddy who you DO NOT have a strong bond with you yet OR go out hunting for a third girl in field - HARD but doable.
BOTH WILL REQUIRE TONS OF SEXUAL OPENNESS AND TRUST.
TRUST TRUST TRUST.... THE MAGICAL WORD HERE.
This older post may help you
However I did not emphasize "trust" enough in this post, since it did not cover having a threesome with your GIRLFRIEND. Just ADD "trust" to the equation and more-or-less everything in this post is applicable to your situation.
You can find even more advice here - although this post covers a cold approach threesome.
Best,
Alek