4 months since upgrading FWB to LTR. She's very inexperienced when it comes to relationships so I've given her the benefit of the doubt whenever it came to sussy behavior. She's been chatting with a guy (let's call him X) for the last few months who seems like a wimp and who I don't really perceive as a threat. Yesterday night we had the following text conversation:

Her: "I'll be meeting up with a few "friends" from uni tomorrow night, can I sleep at your place afterwards? I'd be there at about 1am" (with some emojis)

Me: "since when do you have "friends" in uni? but sure, you can come over"

Her: "I was invited by a girl I met once, and X is there - so more like acquaintances"

Haven't responded since. Two possibilities:

a) She's genuinely autistic and doesn't see anything wrong with going to a meet up with alcohol involved and a guy who obviously has a crush on her, without me, or

b) she wants to fuck him and blame it on the alcohol / peer pressure.

What's especially bugging me is that I'm obviously not invited. If your LTR gets invited to a late night party, her first reaction should be "can my boyfriend come too?", no?

Worth mentioning, she doesn't seem like she's looking to cheat. She's always the one to schedule our next date (two times a week, overnight), we have sex 3-4 times every time she comes over (mostly also initiated by her), she pays for our dates, even my part, never once started a fight or even argument, and she's very clingy whenever she's with me.

So what would you make of this?