As usual the answer is everyone's to figure out their way for themselves but my two cents... This IS more about multiple partners then bisexuality. I'm not openly bi. I much prefer women. Meaning, I can go without dick but I cannot even imagine giving up women. I want a relationship with a woman and I have no desire for one with a guy, it's just sexual. I'm fine not telling a gf I'm bi because I'm happy to just be with her and there's a good chance it will end/change things. Past sexual partners don't need to come up. The past is past, only the baggage you bring with you matters. Ideally, I want to be totally open to my girl but that's just like, ideally, everyone should understand and accept our differences. Now if you want bi threesomes or moresomes, or a gf and bf, or some kinda triad or open relationship...you are searching for a super small subset of women. Gotta do that from the start and be open about it. The chance of randomly dating a woman up for those lifestyles is lowwwww. The kinky sides of dating sites and fetish/swing clubs are your friend.
My brother said something to me about proposing to his wife. Don't propose unless you know she's going to say yes. I've used that policy with women I've been seeing regarding telling them I'm bi. If I meet them online or somehow safe to just be bi up front? Done. If I'm dating a woman and there is some in-route to talking about gay/bi stuff? Cool. Find out how they feel. Two tips, bi chicks mostly are not cool with bi men. HAHA. Older woman seem more in to bi guys but the odds are still slight. I've only known two woman under 22 up for mmf and they were just up for anything. I think odds are almost zero at 18 and they barely get to a half a percent by 30.
Only the few exgfs, fuckbuddies, and couples I've done bi stuff with know I'm bi. In general I think people freak about bi guys. Most people aren't cool with the man on man sex. Lots of people are in that he's gay but fooling himself category and I've even had other bi people flip out cause I'm not bi enough (don't like kissing guys, picky about anal). Don't be with shitheads and you shouldn't get outed. But if outing you will benefit them, I think a fair amount of people will...so yeah be selective or you'll be lying rather than just keeping quiet.
Only one woman I was seeing freaked when I told her but she's the reason to keep it quiet. I was seeing her only about a month. We both had huge sex drives. We talked about sex a ton: threesomes, big dick and even some gay/bi stuff. I was sure she would be ok with it, even if she didn't want me with guys. Wrong. She acted fine with it. Then left kinda quick and stopped taking my calls. No big loss but I was shocked I read things so wrong. You never can tell till you open up and she was a cool chick to lose. She ended up pregnant by her ex like two months later so I think I actually dodged a bullet. HA.
Oh and no pics of the bi sex. Then you at least have the option to call someone outing you nuts.