This is the script Judd Apatow should have used for Knocked Up.

keep it, give for adoption, and/or tell the person

This would make a good movie.

At least it was both of you?... your wife should probably take a pregnancy test too, come to think of it.

It's probably a good idea to start discussing what your options are now, because I believe that you are too far along for an abortion for anything other than life threatening medical reasons.

Assuming the threesome included her wife since it was drunk

technically, late term abortions are possible. it's risky, but it's doable in some states. however, it's probably not the option to choose. if OP doesn't want to keep the baby, adoption. however, this is a great way to have a baby in a same sex marriage without paying for IVF

I bet you’re wishing you’d just had a cucumber now aren’t you?

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They are both the female side. Your comment was stupid.

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Yea, now I'm assuming that you're just a troll, trying to get a rise out of people.

If she is pregnant, she likely is a female

So, is your wife pregnant too?

Did it not occur to you to have the third member of your threesome use a condom?

Could be possible they used a form of protection and it didn't work though- nothing is 100% fool proof.

Broken condom, or they were possibly too drunk to care? who knows without input from the Op.

How did you not realize it after not having a period for more than 3 months?

Some women don't have regular periods. I have a friend who only has three or four a year. Some women mistake spotting for a period. Many reasons to not know, especially if you aren't trying.

I call bullshit too. There's no way you can go 5 months and not be suspicious. I've had 4 and I tell you, there's no mistaking it. When shes starving hungry and experiencing changes in libido after sex with a man and it takes 5 months to put 2 and 2 together? A missing period isn't the only indicator of pregnancy.

Well that’s a story for when the kid is 18. Oh and congrats ?

Ok, here's my two cents:
1) While it was a drunken threesome, as you say it was, you say we (meaning your wife was present) so there's no indication of cheating on your part (IMHO).
2) As people have said, here and on Facebook, nothing is 100%. You could be on pill and him with condom, and still get pregnant.
3) 5 months is pretty far along for an abortion, so if you can't/won't raise the baby, the adopt out.