<human>: Provide a brief overview of the text.

First off, this is (obviously) a throwaway. 

So a little backstory, been with her for 3 years and I love her more than anything. No real problems with our relationship, and to be honest I've never felt this kind of annoyance or anger towards her before. Frankly it feels weird.

Me and her haven't had sex in a couple of months-I should stress, this is not an issue-she was going though 'some stuff' (intentionally left vague, sorry) and we've been taking it pretty slow since then.

This has all been fine until just tonight. I follow her on Tumblr, and occasionally I see her Roleplays pop up on my dash. For those that don't know, this works by people reblogging a starter and adding their part of a narrative, and so on. 

Usually it's all pretty tame stuff, but to be frank, she's roleplaying a threesome with two other guys. I know it's not cheating or anything, but it's hard not to take personally when the girl you love doesn't want to have sex with you, but seems fine doing it with some strangers online.
<bot>: GF is RPing a threeway on Tumblr, am I justified in being pissed off, and how should I tell her?