Facebook for jailbroken iPhone? Cydia?

Okay so I bought my iPhone 3GS second hand: P (well technically it was bought for me). And it was jailbroken when I got it… Which means I haven't been able to update it since last Christmas. -.-" (3.1 = not cool).

Anybubbles… FB doesn't work on my phone anymore *sob* not the app or in safari… Is there anything in Cydia that could help me in these disastrous times! (basically I've used my monthly contract in 1 week… So FB is my ONLY form of communication).

Also… What's the highest I can update my phone to, cuz someone said it was 4.2.1 but all the apps now require 4.3 FML or what!

Laaaastly. If I do upgrade it… How do I do it? I know for my last iPhone I had to pay for it… But it's so expensive! Can I do it myself without killing my phone?

Thank you! Xx

Added (1). So I deleted and reinstalled and still nuthin' D":
I can't unjailbreak it or it will lock to stoopid O2 and I'm not on that! -.-"

Help (for 10 points and kissesssss) xxxxxxxxxx

Delete facebook then download it agin

I would phone O2's helpline and ask how much they would charge you to send you an unlock code (it's usually around £20-25)

Then, if they say they can and you are okay with the price, they will send you an unlock code.

When you get it, restore your phone to factory settings, (or just update it as this will wipe cydia off it too.)

and type in code and away you go…