What if I get too tired to continue but my friend wants to carry on climbing?

Stay together and descend. The entire upper mountain is glaciated, which means that there are crevasses and the party should stay roped together because of this. You also need to look after each other as people suffering from tiredness may slow down and are especially vulnerable to Acute Mountain Sickness (AMS) induced by the high altitude environment. The only proper cure for this is descent.