Am I overreacting about my (19F) partner's (19M) female friend whom he talks to daily? I fear he is dating me because I resemble her closely, and he originally liked her.

A bit of context, he has known this girl from his highschool for a few years I believe, but only got much closer within the past year. I've only been seeing him for a few months, so I don't believe its my place to have a say on friends he has known longer than me. I trust him to never do anything that would involve cheating on me physically, but I'm less sure about the emotional aspect.

On her older posts of her selfies, he would almost always comment things. He would basically be the only guy in her comment sections of over 50+ comments per post, and they'd sometimes chain the comments. He did something similar when he first started liking me, where he would like and reply to my Instagram notes and find any opportunity to start a conversation when I've barely ever even spoken to him in person (classmates); it made it easy for me to know he was interested in me. This seems completely normal, because I occasionally comment on my friend's posts too.

However, she looks almost identical to me in an eery way. We both have pastel pink hair, both asian, and even our faces look almost identical... I recently cut my hair because he told me he loves short hair (she has short hair). Both she and I do art, and he has recommended me to switch to a psychology major because he thinks it suits me better and I only recently discovered that she is also a psychology major. She goes to a university in another state so dating her without being long distance would be impossible for him. He told me his original dream university a while back, and I just realized it was the one she went to.

Some of her stories tag just him on what appears to be dessert dates. He still texts her every day, and when he shows me videos on his phone I see banner notifications from her messages actively popping up. I know all of this could be coincidences, but I can't help but feel like I was some sort of second-choice or just a girl that reminded him of the girl he really likes, and that he is molding me into resembling her more. He isn't the type of guy to ever make the first move (I was the one who asked him out despite him liking me first, and he said he was grateful because he never has the confidence) so it's possible that he always had a crush on her but she was either unattainable or never liked him that way back. She also got a boyfriend recently, but she has a poor relationship with him and complains to my boyfriend about him.

Maybe I'm just overthinking, but I feel like its possible that my boyfriend has always liked her but circumstances prevented him from being with her (such as distance and her not making any moves). This means the chances that he can cheat on me are low, but I wonder if it's okay to let him keep talking to her every day knowing he used to like her (and might still like her)?

Every now and then he will bring her up in a conversation as "my friend" and never say her name, but he mentions what school she is from or other details that make my heart drop knowing its about her. I know I should communicate my uncertainties to him, but I also don't want to seem like I don't trust him because if I'm wrong, that will hurt him too. I deeply love him, and I constantly feel like a burden in his life already. Outside of this, our relationship has been very strong. I am most definitely just overthinking this, but let me know what you guys might think!!