Girl needs advice lmao

so i’m having this problem when my SO and I have sex it’s so great in the moment and then he finishes somewhat fast and will just be the end of our sex. I’m not really satisfied after. I’ve had a conversation with him about 5-6 months into dating that maybe he could go down on me after he’s done so I could feel something alittle while longer or even hopefully cum myself. It kinda makes me upset he just finishes and then that’s the end of it. I also don’t want to make him do anything he doesn’t want to do, it’s a weird situation for me. He can see that im upset after because he will be like “i’m sorry I came fast I can’t help it you’re so wet”. I need help getting through to him without putting him down. The sex is great it’s just not leaving me happy at the end. HELP HELP HELP. I don’t know what to say to him in a polite way.