Wanting to have a threesome or a foursome with another couple BUT THEN....

So I (24M) and my girlfriend 25F had a discussion a long time ago about having a threesome or a foursome with another couple, she was more inclined towards another couple than a MFM (I was more okay with MFM coz my pleasure is all about making her feel the best). We discussed, and then started our search, we thought it will take months to find people but turns out there are many waiting for a good couple and we found a suitable couple in less than a week. This made us too overwhelmed and we decided to drotthe plan as the couple was not like us, and the girl was secretly messaging us to ditch her guy and have a FMF Instead.

The experience was not that good and smooth so we got busy with our monogamus life and never had another discussion on the topic. Now after a long time I'm again getting those kinky urges to have a threesome, so I've decided one thing, as me and my girlfriend are working out to build a good physique, I'm thinking about making our threesome or swinging/foursome as a reward for our goal of fitness.

I want to discuss this with my girlfriend, so that we both are on the same page.

What do you think about my idea?

P.S. during our search for another person/people, my girlfriend got a little scared with the idea (maybe she felt that as it was all getting too real), although it was her idea to have a foursome instead of a threesome.