First LTR so far

Title: GF eyeing other guy

It went so fucking good while we were waiting for all people to get together so we could enter the bus and start our journey. Until we entered the bus and i noticed how she turned behind all the time.

I figured out that there's the dude who was sitting behind me. When i jockingly mentioned how she's turning a lot she was ' im just noticing how young our group are' (there was bunch of oldies and then us, younger ones), but i felt something was off.

First of all, she would spike fast glances behind mine and her seat, apparently i guess, looking at that dude. Then she would drool over me, kissing, resting her head, cuddling and when she was getting back at hers she would glance, those ones where she thought i wouldn't pick it up, but i did obviously. I guess once she literally threw arms at my head so she could look at the guy.

All of it made me paranoid. I immediately shut off and withdraw feeling betrayed and extremely bad that i didn't know what the fuck to do then. I couldn't look at her, when she was touching me i would just move and ignore, this shit broke me. And i had those feelings for 4 days of how much we stayed together. I couldn't relax, be in the zone, be myself and outgoing. I just froze and close myself and whole trip was shit to me because of it

I have few options then:

First - break up with her

Second - upgrading my SMV and working harder!

Third - dreading (im bad at this if someone can guide me a little)

What do you think from all of this?

I'm looking at other chicks, now i feel awful when roles are reversed. Is it my insecurities or my instinct and gut feeling speak truth?

edit; it got me thinking what would happen if i wasn't there? They haven't talked, he wasn't looking at her, she was the one!