Hey mama! I'm a breastfeeding peer councilor, this is a super common issue with babies! I would recommend helping him by squeezing your breast a little and like @kambam mentioned, put your nipple near babies nose. Usually them smell it and want it so they open to find it. If that doesn't work, my next question for you would be if you've had him evaluated for lip/tongue ties?

he only is taking half and it makes me get cracked nipple...

If you place your nipple on top of his top lip he should open wide to take it