Hello all and thank you for taking an interest in my question.

I am 24 years old and I am currently in a relationship with my girlfriend for almost a year now.
Several months ago, I jokingly made a comment about having a threesome with another girl. This did not come up for a few months after that, when a friend of mine said something about a threesome in front of my girlfriend and I. Later, while we were discussing the matter with my girlfriend, she said that she was recently thinking of experimenting with another girl. Numerous times, she has commented on a specific girl, which for the sake of anonymity I'll call "M". This girl is a very good friend of my girlfriend's and they talk about sexual stuff all the time. She told me that if she ever had a choice to do something with a girl, it would certainly be her.

Later, a couple months after that, during a house birthday party, my girlfriend and her female best friend, french kissed, multiple times. Probably worth mentioning that they were both 100% sober and I was present during the kiss. My girlfriend later apologised to me numerous times for making out with her friend. I let her know that it was OK, and it was actually a turn-on. After that event, she kept bringing up the threesome conversation, as if she wanted me to do something about it.

Anyway, a couple of months ago, we were talking about my girlfriend's friends, and "M", came up. I wanted to see if she was actually interested in experimenting with another girl so I asked her if "M" was dating anyone, and one thing led to another, and well my girlfriend and I started talking about the possibility of having a threesome, with a basic rule that I wouldn't have sex with the other girl. At some point, I realised she wan't entirely comfortable with the whole thing, so I let it go and decided to forget about it as I didn't want to force her into something she wasn't sure of.

And now to the point. A couple of weeks ago, my girlfriend started talking to me about "M" and how beautiful she is and that she wouldn't mind experimenting with her. I wasn't sure what she meant so I tried to make a joke out of it to get a serious answer, so I said it would be fun if we could all work something out together, and she seemed to like the idea.
So my question is, is this an invitation? Is my girlfriend trying to make me ask her to have a threesome with this girl?

What are some ground rules you think I should be prepared for? How do I approach my girlfriend on this to make sure it's what she wants, and if she's not 100% sure about it, how can I convince her? Again, I don't want to make her do something she's not sure about and I certainly don't want to force her.

Thanks!
Evsdroppr

She's your girlfriend - ask her if she's serious or not. If she is both of you need to sit down and set some guidelines, expectations.

How can you convince her? You basically can't.

I'm confused. You need to convince her BUT this is something she wants - ?

She keeps bringing it up so I'm led to believe she wants to have a threesome. But whenever we have a discussion about it she seems to slowly let it go as if changing her mind.
She obviously likes the thought of it, but I'm not sure she's quite sure about it, so my question is basically how can I let her know that it's OK, remove any insecurities she may have, and convince her to do it?

Know what I think? I think she wants to mess around with "M" and is just looking for the 3 way as an excuse to be able to get to do it without feeling guilty.

I agree with Odinn7 - and I repeat, she's your girlfriend. Stop second guessing her and ask her.

I would also define a three some. She's going to have sex with the other woman and you; the other woman is going to have sex with her; you are going to have sex with your girlfriend. Then the negotiating about "what is sex" happens.

Oral? Something else?

I am confused as last year you were 20, and a few months later you are 24,

https://www.askmehelpdesk.com/relationships/should-do-597554.html

What gives here??

Good catch - if it helps OP was 17 in 2009 (3 years ago). Let's see, 17 plus 3 = ?

Your GF is showing interest several times but the missing piece is your opinion, meaning are you willing to have this 3some with M? If so, inform your GF of this as "M would be one I'd include in this as well". Talk to your GF about the hesitation as well.

This happened with my partner and I , it was a great idea but once it happened I hated it, he spent so much time sexing the other girl I just felt left out and unimportant.. if you are going to do something like so, make sure your main focus is your girlfriend.. Let M and your girlfriend start, see where things go with them, if your invited into it remember your relationship/gf are more important than having sex with another girl, sorry I can't give advise on how to approach the situation, but at least you know what to do if it happens.