Yup, Ganguro's got a point- are you clear on what you expect from it?
Do you think you might 'switch' completely to being a lesbian?
Would you say your attraction is mostly physical or emotional?
Would it feel like cheating?
I couldn't tell you how it would affect all the relationships you describe- mostly because I know next to nothing about you or those relationships.
I do think it will cause some stress. You seem very concerned with the possible consequences, so you'll worry alot
Rule number one is
to keep communicating
If she has an open marriage, she might have (had) several sexual relationships [who also have several] and then there's no telling how safe things are.
However, if her husband is healthy...
Anyway, it all comes down to trust, I guess.
How would you feel if you'd just cuddle with her, both fully dressed. Something on the edge of your comfort zone, but not beyond it.
Just take it one small step at a time, that way you'll all have time to catch up with your emotions.
It does sound pretty exciting though, I hope you're enjoying it atleast a little bit
