Ditzy:
If she is doing other guys how is she your girlfriend?
Jsmjsm:
Simple, because we both agree on it.
I'm sure you don't need me to tell you this, but I think you were in the right here, Jsmjsm. A relationship is more than just sex. And from your second post it sounds like this is something she initiated. I think it would be hasty to judge that you had convinced her into this as some of the other posts imply.
I'm going to proceed under the assumption that she wanted to try to have sex with this other man in the first place and that's why she brought it up, and in the end
you enjoyed it more than either of you expected.
The fact that you were both communicative enough to negotiate this with mutual consent is a good sign for your relationship; it seems unlikely that your fear of losing her over this would come to fruition as long as you continue talking about these things in the future and respect each others' boundaries.
I will gently suggest another alternative to leaving cuckolding in fantasy only. There are many people who are in relationships with someone with whom they don't share every kink and fetish; there are plenty, like me, who are on this site because our partners don't have an interest in feederism but are supportive of us pursuing it in more than just fantasy.
ENM can allow people to explore those tastes. It seems you're already practicing it, at least a little, if you and she agreed on her having sex with another man. You can apply the same to cuckolding. Talk to her about your options for exploring this kink with people outside of your relationship if it turns out to be something you can't just leave in fantasy without distress.
