SUCKING DICK, HELP

i need advice about sucking dick please help!!!! I’ve been doing it to my sex partner for a long time but i just feel that I don’t do it well because i feel that my teeth touches his dick sometimes. Is it normal that after being a couple of minutes doing it my mouth hurts? And the last two times, he wanted to come out in my mouth but he couldn’t cause i stopped every time my mouth was hurting and he told me to not stop but I couldn’t keep going, so please, any tips on how to control my mouth from hurting and my teeth? And do guys like when we spit their dick?