i 24f need help not overthinking something my bf m21 said ?

my boyfriend and i were having a normal conversation when he randomly said “i would never cheat on you” it caught me off guard because i thought it was a weird thing to say, especially out of the blue. i told him that it made me feel weird and that i was probably overthinking, but it made me think he did something and was coveting up a guilty conscience. he got really upset with me and sighed and rolled his eyes and said he didn’t want to talk about it and that i was trying to make him feel bad. i told him i wasn’t, but that i’ve been cheated on (he knew this already) so im very sensitive to the topic.

im not sure if i am overthinking or if i actually have something to worry about