JaJa, when reading your post what's most interesting to me is that you are more concerned that you may be bisexual, rather than being worried that your husband desires sex with another woman. That says to me that you are reasonably secure in your marriage.
"but i am so scare to do this, thinking i mite like it since i have a thing for girls"
My opinion is that you are extremely curious about what it would be like to be with another woman and your husbands 3some desires provide you with an excuse to discuss your feelings. I'm not going to suggest you try this, but I will tell you that many women (and men also) have an overwhelming curiousity about same sex sex, so your feelings are not unusual.
Here's the guy point of view on your husbands 3some desire. Many men can't imagine anything more exciting than being in bed with two women. That, in itself, does not mean he wants to be with another woman, because he doesn't need a 3some to do that. If it was as simple as that he could have an affair so I think this glass is half full.
Since we're just chatting here, how would he feel if you told him your fantasy was to have a 3some with two men. If you get, as I suspect you will, a negative response, then you can reasonably ask him how are you supposed to feel when he says he desires sex with another woman.
I know, this is probably not realistic but it's fun for me to think of his reaction to this suggestion.