blowjobs

ok so my ex was my first for everything and we had sex and everything else way before I was able to give him head. I thought it was because he was my first and I was unsure of what to do and all that. but now I'm with a new guy and we've had sex and he's gone down on me and I'm feeling held back. I can't bring myself to give him a blowjob. he won't admit it but I know it bothers him a little. is this normal? does this happen to any other girls? how did you fix it?