I'm not a woman, but I can give my own point of view. I've never tried a FFM threesome with a girlfriend but I have tried MMF many times with a couple of various girlfriends. I'm not the jealous type, so I never had an issue, but they didn't seem too keen on sharing me with just another girl. Once I had tried swapping with another couple, but my girlfriend at the time didn't like the outcome afterwards. The only time I have had a FFM was with two girls I met at a bar in Brasilia, but all the MMF were incredible!