Great topic Artchic528!! I certainly don't have a great answer for you, but just my opinion.
I think there's bj's that start things off, that move on to other things. These bj's are short in duration for you. I'd say if your jaw is getting sore then switch it up with your hand....& tongue....doing other things & be aware of how your partner is reacting to it.
If this bj is supposed to make him ejactulate....& your not sure of the taste then maybe keep a towel close by if you need it.
I had several bad experiences that have led to messy cleanups & my immense embarrassment. But I did learn for the next time. I learned to talk while I was...down there, so I'd know what my partner wanted.

With my SO I've never really been fond of the act myself & always feel obligated.
But with my partner the dynamic & feeling is totally different, in every way.
So take your time & see what ur partner likes, but also even more importantly, what you like & what you like to do & offer that feels good to you too. You should be enjoying the process just as much as your partner.
Have fun too!