I concur. This was definitely a big screw-up on her part. If she knew before-hand that you had no interest in men whatsoever, and yet took advantage of your inability to see what was in fact happening, then I don't see this as being any different than a man who plies his girlfriend/wife with alcohol to "loosen up her inhibitions", coaxing her to do things she otherwise disagrees with. Like you said, now you've got this image in your head and you can't shake it. "Thanks for the memories, honey."
This doesn't necessarily have to be the end of swinging or anything. This is one of those inevitible screw-ups that we all make when we are learning about "schoolyard politics." You'll make a mistake just as enormous, most likely, simply because you won't have realized just how hurtful it was. So it makes sense to be understanding towards your wife; she may not realize just how damaging a thing it was that she has done to you and the level of trust you have in her. "Having a backbone" is one thing, but without flexibility, you're just going to get hurt.
Do NOT allow yourself to be pressured into sex that you don't want to have, no matter how much it turns her on. Let her know that you do want to please her, but she cannot ask you to compromise yourself in this way; it is simply unfair. She might've been turned on by male homosexuality, but you absolutely are not. She's bi? That's great! Good for her! She just needs to understand that you don't "learn" to be bisexual. You either like it, or you don't. You don't like it. End of story.
EDIT>> Just a thought: would you be comfortable having a foursome with two other bisexual guys? Maybe your wife's friend and a friend of his? This way, she can watch the other two get it on without you needing to be involved. This may not work, though. If she still doesn't understand that it is not okay to coax/plead/beg you to try it...just this once...just for her...you won't like it. Or maybe even having bisexual activity happening around you might be enough to make Mr. Happy go into a coma, I don't know. Again, if that's the case, then forget I said anything.
That's just one idea, though. Perhaps you can come up with a creative solution where your wife's interests are satisfied while yours are protected. Best of luck!