Boyfriends past

I know this sounds stupid and I'm probably overthinking because I'm hormonal and emotional because of my period right now, but I just realize that the only other girl that my boyfriend hooked up with and his only other ex girlfriend were both on the bigger/ chubbier side. I myself am not a size 6 girl, I've got curves to me but not all the right ones. I'm not quite plus size but I only just got the biggest size in your average clothing store (12-16 Canadian) and I'm worried and wondering now, is he only with me or did he only go out with me in the first place because I'm not smaller? Is it only because I'm kinda bigger?