Struggling with My Girlfriend's Polyamory

so hi, back again. really just need to ramble about what’s on my mind cus it’s driving me nuts being unable to talk abt it with anyone so just a couple days ago, my girlfriend was on call with me and we had discussed about her feelings about them being polyamorous. i was able to help her through the night and she came out to me as polyamorous. now me, im fully monogamous and i’m too scared to even consider questioning that side of me at the moment, but for right now i just know i don’t want that kind of relationship. they tell me it’s mainly just crushing on others and that she doesn’t want a poly relationship at the moment, and i thought i would be comfortable with it. for some reason, though, i’ve just been struggling to come to terms with it. i have nothing again poly people, and it sounds stupid but it makes me feel like i’m not enough for the relationship or that i’m not the one that they want. we’ve been together for a while and it’s genuinely really scary to me but i have no clue what to do or how to approach her. she’s been in a bad state of mind herself and she can’t handle anything too heavy, so i typically just take their baggage and deal with my own baggage. she’s told me about the others she’s crushing on and i’m scared im falling behind in some way because she hangs out more with them or i’m not cool enough like them and it’s stressing me out more than ever. i feel like it’s selfish for me to feel this way though, but it’s just really hard for me to deal with. feel free to message me if anyone has advice