[Additude]

What your feeling is not an unusual emotional feeling. It's really a conflict of social programming (not saying that is a bad thing) and your personal doubt, fears and trusts conflicting with what your mind tells you is your "standard practice" and normal thought.

For example, if you and everyone else in our society grew up with the concept of swinging, that it was acceptable, that either spouse, with the knowledge and permission of the other spouse could venture out sexually and return home to their husband or wife, etc. and it was no big deal, you wouldn't be having these feelings unless something was different to that normal thought process.

My point is it's all about conditioning. As you stated earlier, your foursome was nerve wracking to begin with, but after you went thru it and experienced it and had fun, you actually ended up appreciating the experience....you ended up trusting the situation, trusting your own feelings and trusting your relationship even more.

That's where you need to go next, trusting this new experience, trusting yourself, trusting your relationship. Your boyfriend is not telling you his fantasy thoughts because he hates you and because he wants to hurt you. He is telling you those thoughts and feelings because he loves you and trusts you and wants to share his inner-most feelings with you.

Be less afraid of damaging your relationship and more trusting of embracing and building an unbreakable bond in that current relationship.