Will a threesome ruin my relationship?

I would talk to her about it, if I was your girl I'd consider it

If she's cooled off, you don't really have a choice to make. She's not interested anymore and pushing her into it is going to make her unhappy and resentful and possibly ruin your relationship. I think you've missed your opportunity.

If you're thinking of marrying her, you better talk to her about it soon. You don't want it looming over you after you are married.

Well. I think that your relationship will be ruined if you do that. Womens can be more than "open" and allow thinks. But when they are in the "fact" they can act in a strange way. Let`s face it. They are WOMENS. We never know how a women will react in a certain situation.
if you still want have a threesome. You should have it. But not in the same bed and far away from the person you love.

I will tell you that I've never had a threesome, but me and my girlfriend have thought about it, we even have gone out looking for candidates, we were out one night and we found one, as soon as I saw the look on her face when she saw me touch another girl, I could see how uncomfortable she all of a sudden was. I love her too much to see her like that. We didn't do it. I don't recommend it, it has a huge chance of ruining the relationship. If you really love her, just be happy with her and her only, I hope this helped