Help w/ My girlfriends obsession?

[Travis]

My girlfriend of 6 years has recently developed this strong obsession for some British actors. Every time I bring this up as a problem or an issue I'm having she gets über pissed and defensive & we only temporarily resolve this much larger issue.
The other thing thats got me worried is she has acquired some new female friends in London who share this same obsession and she has been telling me that she wants to go there alone on her own trip w/out me (what's weird is that whenever its brought up, she ALWAYS emphasises that she wants to go on the trip ALONE).
I'm ok with her having her own experiences, but in this instance there are ALOT of red flags going off in my head!
1.). Why does she want to go to a country to meet friends w/out me?
2.). Is going alone just an excuse to cheat on me w/ someone she possibly met online?
2a.). I bring this ? Up cause a few months back I found a video in her gmail inbox (I wasn't snooping I was looking for an old email that she sent me that I had deleted and needed to get again), but I found a video of this dude, who resided in the UK, well he was jerking off for her and telling her things about himself, idk I couldn't finish it.

I don't know what to do or even think here! I love her so much!
I mean help me out here:
Should I be worried?
What questions should I be asking her?
Am I thinking too much about it all?
Is my thinking of her obsession, then her meeting these friends, & them wanting to go on a trip, am I thinking way too much into it (like making a mountain out of a molehill)?
Or
Is my gut instinct of the entire situation the 1 I should follow or not?
What should i be doing or saying?
I'm trying to understand this I obsession but I can't & I'm lost & don't know what to do, there are so many variables here that's its just left me, well to be honest it's left me exhausted
&
as it looks right now our relationship is sinking because of this obsession. Any advice would be appreciated! Thank u