Retroactive jealousy

sooo!!! This is going to be a long post, bare with me. Im in a relationship with a guy, 2 months, been talking for 3 months and we already have a crazy bond! We talk all day, everything is going almost perfect, besides some small problems lingering. However, he was the first i guy i have ever had sex with, and he has done it with 2 other girls, which with one he was also in a relationship with. She and I share the same name. He has had almost all his firsts with her, while all my firsts were with him. He always tells me he loves me and i honestly believe him! I know he likes me and I know most of the things he has felt with me, he has never felt before. But that girl, ugh that girl. She always lingers at the back of my head! They were in that adolescent relationship stuff that all people have in their 15s! Where it is one sided but the other one is seriously struck in love… anyways. Today we were scrolling through his old messages and i saw a name, it said “in laws”. I asked who is that and he said oh um my exs mom, i laughed but then it seriously struck me, man maybe he still thinks of her. Then it all went downhill. I just became quiet and more aware of what was happening, analyzed the tone in which he said that trying to find any kind of emotion but all i found was sadness. He was a explaining a little about the messages and told me a story, about when he was with her and their old friend group sitting somewhere and they had just broken up. He put his hand on her thigh and asked her if they can talk somewhere private. Then he said to her that hed change and become better. Back to the present, he proceeded to say “ then i just pulled her close to me and gave her the best kiss i have ever gave someone, in my life, ever.” Honestly I didn’t know how to react. I have never been so jealous and this isnt me but im seriously hurting hearing all that stuff about them. I just have a bad feeling. The lingering feeling of dried up love he has for her.