No, it's not different because it was a man. Not one bit. (He knows this...that's why he did it behind your back). He's compartmentalizing. I'm guessing your vows weren't "forsake all others....until I'm ready to explore my sexuality...." 
"Bisexual" means capable of being attracted to both sexes...not *needing* both sexes for survival.....and, as his wife, *you* should be his priority. 

There's a quote that makes the rounds here quite a bit....."You do not have to set yourself on fire to keep others warm." Listen to your heart & gut on this one. Six months is not nearly enough time for your head to catch up.  <3 
 

Sonata—I can really feel your pain. I, too, would be devastated if my husband asked for an open marriage. 

For an open marriage to be successful, I firmly believe both parts of the couple need to be fully on board with it. As you mull this over, I think it's important to take the bisexuality out of the equation...because it's irrelevant (in my opinion): Would you be OK with your husband seeing another woman "a couple of times a year?" 
 

There's not a whole lot of sexual content in the Married and Bi community...and the moderators are pretty quick to remove the random dick pics and hookup solicitations that pop up...but I did want to warn others that there's not a big straight spouse presence in that forum...and some of the conversations may be "triggering" (for lack of a better word).

ExBeard wrote:

Knew I’d seen it somewhere. See link to full article and relevant text below. Hope that helps! 

https://www.theguardian.com/world/2019/nov/03/did-i-ever-really-know-him-the-women-who-married-gay-men
’Did I ever really know him’?: The women who married gay men. 
Some reactions are more surprising. Service manager Roxanne says a post-disclosure honeymoon period can happen, and sex begins again because it brings back emotional intimacy. Such was the case for Madeleine. “Interestingly, after it came out, we had a brief spurt of sex together. The first time it happened, I cried. It had been eight years.”
 

The post-disclosure honeymoon period is so common...I think it is probably a trauma response...Ideally, I think the straight spouse should have some distance post-disclosure to think clearly and process...Of course, that's not practical for most people....especially when there's children involved. Has anyone come across any good studies on "trauma bonding" (in this context)? 

So nice to hear you are doing well, Chalizbet! You seem like a very caring & thoughtful person—and your partner seems more empathetic and honest than most we hear about in here. My husband and I are still together, too....(together close to 10 years; bi bomb came during year 9 on his 35th birthday). The dishonesty really eat away at me at times, but I'm trying to make it work [while keeping my guard up ;) ]

I've also discovered the Married and Bi subreddit...but haven't found it a great resource for me, personally..Many of the posts are from bi men struggling with monogamy (which just feeds my paranoia)...I was actually banned from posting after responding to a man who was cheating on his unknowing pregnant wife with multiple men (the admin flagged my response as "shaming").  Still, I check it out from time to time to get insights from "the other side." Though, with the nature of it being the Internet, I understand that the happy monogamous types probably wouldn't find a need to be posting online.

The "straight wife" blog was really helpful to me during those early days (www.thestraightwife.com)...Even though the outcome wasn't great (they opened up their marriage and are now getting a divorce)—the humor provided some much-needed light during that very dark time. 

I'll check out the other community you suggested.

Thanks again for checking back in! I hope you stop back in from time to time.

Warm wishes,
J <3