is there something wrong with me?

why is it that every time a relationship with someone starts to get serious i get super bad anxiety just at the thought of them? this first happened with my ex and i just thought it meant i wasn’t that in to him so i ended it but now it’s happening again.

for the past few months i’ve had a thing with a guy and it’s been going great and i really like him and he likes, but about a week ago this anxiety thing started happening again, something as simple as thinking of him i get this nauseating feeling in my stomach and my anxiety kicks up, things start looking different to me and feeling different, i freak out when he wants to see me and my mind tells me to end it. but i really don’t want to, i just want to be able to properly enjoy what i have with him.

i’ve been trying to figure this out but the only thing i could possibly think of is a relationship i had when i has 13, i don’t know if maybe my mind is trying to stop me from getting attached so i don’t get hurt so badly again? but then i start thinking that that’s stupid because i was so young that it barely counts.. does anyone have any idea what’s happening here?