I'm not going to address the relationship stuff as that seems to be covered.
But from an technical standpoint regarding your computer and stolen data.
Back up your photos and other things you want to save.
Then you nuke your computer, I recommend a wipe+clean install as some nasty programs can survive a normal reinstall. I'm guessing the logger is a software, but it could be hardware. Look for anything attached to your computer that you don't know what It is.
Change your passwords, secret questions etc on everything and I mean everything.
Haven't used an account for a while (since before the keylogger), if it does share a password/secret question with any other site that has been compromised, then it's compromised as well. Have an old email that you don't use? That could potentially be used malicious. Change password on those to.
As we don't know if she has installed anything on your other devices I'd also recommend nuking your phone if you have a smartphone, I don't know how/if this applies to stupid phones.
Better safe than sorry, so I'd nuke my router/modem/switch as well (I believe a factory reset would do)
I would also speak with my bank, what damage can be done from knowing only my account number? Is it sufficient to only change login information or will you need a new account?
I know nothing about (assuming you're American) social security numbers. Will you have to secure that aswell?
Then when potential future damages have been prevented, I'd file a police report. I'm not saying you should as its up to you, but I would have. If you want to do so, it might be best handing your computer to them or a 3rd part to secure evidence before wiping it and and destroying all the evidence.
/r/techsupport might be able to help you with some of these things, or give you a better idea of what needs to be done.
What I've written is what I would have done when someone have had physical access to an unknown number of my devices to pant malicious software/hardware as I couldn't possibly be sure my router (or any other device) were untouched.
I'm quite paranoid regarding things like these and have likely gone overboard. But I like make sure no software were left on any device as all password resets would have been for naught if one device is left infected.
Sorry have to get back to work now and haven't formatted my post or spellchecked it.