Do guys forget easily?

I am now dating a guy whom ex cheated on him and dumped him. In the begin of our talking stage he would talk a lot about her. He even once mentioned her family name. She was actually his first love and first relationship ever. I didn’t really like it but tried to see over it because i was interested in him. Now he doesn’t really talk anymore about her. But still i feel weird. I am afraid he is still thinking about her or what she did to him and that he is just using me to find some distraction. In the begin he said that she broke his heart and that he even cried...
I talked to him about it a few times but he would always get angry and tell me to leave past in the past. He says that he is over it but i still have my doubts tbh. he is quite emotional type of guy.
what do you think?
Do guys forget easily?
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