Is it my partner's fault that i cannot ejaculate?

In most cases: no: The inability to ejaculate (to reach a climax) can be due to a variety of causes, but in most cases, the problem is not the partner. Causes include general fatigue, too many ejaculations in the past 24 hours, anxiety about the relationship or other things, fears, increasing age, medicine side effects (such as with ssri antidepressants), diabetes and other causes of poor blood circulation, etc...

What about the rest?: In a relationship, it's not helpful to talk about "fault". If you are unable to ejaculate when you are entertaining yourself looking at your favorite pictures / movies / thinking your most exciting thoughts, then the problem is with your body. If it's just with your partner, then the problem is with the couple. In either case, it would be helpful to get with your physician. Are you taking any meds