I'm going to take a different tack from some of the comments here: I can understand SW thinking (if you didn't make this 3-month lag clear to him [it's a birth control method I've never heard of before]): 'Well, she's safe from pregnancy, we've both been tested for STDs and AIDS (and we're both low-risk because of our normal safe-sex principles and practices), she was using condoms before because of the pregnancy risk, so that reason has disappeared...'
I would say that your 2 biggest mistakes were
a) not making it absolutely clear to him about
i) the fluid bonding (or whatever you want to call it) with your GF,
ii) the results of your STD tests not being back yet,
iii) the 3-month delay factor;
and b) not paying attention (but I can imagine how this might happen - from your point of view / responsibility).
The real sticking point for me is his breaking of his own fluid bonding. As you wrote, "Why would he do this?", and "it literally never occurred to me that he would want bareback sex with me". (And why did he wait until he'd slipped it in before asking: "Is this alright?" Sad to say, but some men do think with their dicks.)
Still, what's done is done, and I think that you should stop beating yourself up over it.
You're not pregnant. (yay!)
You've learned some important lessons. (hurray!)
You're going to have "let's get this absolutely clear" talks with both your men-friends (and - I would hope - any future sex partners). (yippee!)
This is not going to happen again. (loud cheers all 'round)
(There are some poor saps out there who never learn. Count yourself lucky on that score.)
If I can't dance, I want no part in your Revolution.
- Emma Goldman Anarchist and Polyamorous par excellenceThe person who says something is impossible should not interrupt the person who is doing it.
- old Chinese proverbAnd the day came when the risk to remain tight in a bud was more painful than the risk it took to blossom.
~ Anais NinI'd rather have a broken heart / Than have a heart of stone.