I can see why it could be upsetting you love your boyfriend you want to spend time with him yet you feel like he puts a sport above you. But trust me that is not true in the slightest, you have to have something YOU are passionate about that you do for YOU away from your partner , your family etc etc something that you enjoy and that makes you happy this is his karate. Its healthy that he has this sport that you spend time apart so he can do this sport, your partner should yes be the centre of your world but not the only thing in your world.
I have to balance my boyfriend with my sports, I do eventing which means I have to get up at 5:30 am everyday to go muck out my horses and if i have shows the next day I cant see my boyfriend this meant I missed his christmas party as i was away competing up North, that I go away competing with my horses for long periods of time, but he accepts it. Sometimes ive had to cancel dates half an hour before its supposed to happen as my horse has gone lame or has colic but he accepts this, he knows that if i didnt have horses and go away competing i would be very very unhappy. He is also into his football and the gym, so there are many times when he's away playing football or going on football boys nights out and therefore cant see me. And yes it gets frustrating sometimes however its the most healthy thing for our relationship
Imagine if he didnt have a sport and he spent lots of time with you and had nothing else he enjoyed or got excited for, youd get so intense youd both suffocate. Why dont you look into starting a sport or even just join the gym or what not.
Him being attached to his sports doesnt mean hes putting them above you but its giving your relationship a healthy balance you cant expect him to give up something he clearly loves as then he will resent you