Guys, really appreciate some honest advice basically on how to deal with the situation... not necessarily what the situation is (i'm very good at turning off my emotions and want to approach this in the most minimally personally damaging way possible). Been occasionally checking in on the trp subreddit for the past two months since I found it but am not an active participator as I'm still sorting out my LTR and where I want to take it and what I want to do with it and learning the philosophies of TRP.

Here are brief cliff notes * LTR for a little over 4 years. Girl in mid twenties, I'm in late twenties.
* Good sex life even to the day.
* Girl has given red flags over time. I won't get into specifics as I want to deal with this situation as I need to decide within an hour or two how to proceed.
* gf left her laptop open when I was visiting her house couple weeks ago. It was on Southwest searching for flights across the country.
* gf used to have a trainer who did classes when he lived here then moved cross country to the location she was scouting. Ive met the guy hes a nice guy, and I never got jealous worried about him because my girls been satisfied with me and hes quite a bit older (over 40). Didn't seem like a thing but shes always liked him, talked about him being a good guy, going to miss him, is funny would tease her etc. I never paid it no mind because I didn't want to seem insecure and genuinely thought there was nothing there.
* Gf never mentions looking into flight, weeks go by, we go on a vacation I paid for.
* Today get a text like "omg found out something crazy today my head is spinning and I need to decide what to do." I talk to her a couple hours after because I'm finishing up work. Her "So this is crazy but, [her slutty friend] is giving me this amazing opportunity with her to go [cross-country on exact dates she had been looking into] .
* So she says her slutty friend was planning a trip cross country (same dates and times she was searching for on her computer - I think they were planning this together back then) and that her slutty friends, friend, backed out so now the friend is offering her her spot for the cost of the difference between the points and miles for the flight.
* Immediately instinct kicks in, red flags etc. I try to say "oh thats cool, but obviously I'm reacting to this with a shitload of scrutiny, skeptical, and am already ready to push the nuke button on our relationship. This comes across in my attitude although I try not to show it.
* I've played it off, in terms of reacting yet, because I need a course of action. GF has already noticed "i'm acting weird" (this is all based on tone over the phone), so its an emergency situation where I need to decide how to confront it - options I have come up with are

  1. Ask to see her phone when she comes over. If she refuses say give evidence to what I saw and basically tell her to give me my spare key back to apartment and leave for good.
  2. If she lets me look, look for evidence between her and her old trainer friend and if they talked about trip before "the phone call out of nowhere that happened today" (look for that too). If its scrubbed, confront her on that, tell her I don't believe her and peace.
  3. Wait till she leaves - try to act like everything is normal, pack all of her little shit thats left over here and leave it at the door. Send her a text explaining what I saw and how she lied to me thats unacceptable and to not expect to see me anymore when she returns.
  4. Let her go, see what happens, how she reacts, lies more, and do nothing and remain in blissfully ignornat ltr.
  5. Let her go, act like everythings normal, wait till trip is done, tell her on flight back we're done.

Please help. I will check back on this. Appreciate any insight I want to approach this in the most minimzingly damaging way to myself as possible. We have just had unprotected sex (we always do) as of last night (gf on the pill), which is also additional information.

Update +3 Days After OP: Weekend is over. Weird weekend. I have not confronted her, she has not left for trip. Thanks for all the help, advice, and comments. I tried to be as "normal" as possible during every phone and in-person interaction. This has been near-impossible. She knows something is wrong and has repeatedly tried to get me to reveal "what's bothering me". I have not presented her the evidence yet as i've basically narrowed down my options to

  1. Telling her what I saw. Asking to know why. Moving on from responses from that (if she denies, leave... if she breaks and tells me why she felt she needed to hide go from there)
  2. Waiting till shes flying back from her trip to pack up her shit and send her some text about being done.

Have had sex a couple times, she's slept over (this would be a normal amount for the weekend - not more and not less). She keeps repeatedly trying to get my attention/me back to normal (instagram posts of us, calling me, initiating hangouts, etc.). She seems to have hit a wall because I've shutdown and now it's getting to her.

I'll update when more happens. A couple of people have pmed me about it, sorry for being slow but I'm trying to make extremely calculated moves. It's a part of my personality. Thanks again for the help.