This stood out for me as I read through the posts here. Ok you may think that the fact that she's manipulative and wants her own way may be something that invalidates her opinion but I would say that the opposite is true.

What do I mean? Well she is a similar personality which you think is manipulative. She has no stake in this and is in an unbiased viewpoint. There is likely no ulterior motive but.. as a person that may have been guilty of the same behaviors, she may be in the best position to actually evaluate better what is going on. You, on the other hand, have a lot at stake here, you're biased by your caring for him and attachment. You have reason to hope that you're not wrong because well, who wants to be wrong about who they choose to be with? We as humans tend to overlook the obvious especially when we are attached to someone that we love and hope to spend a lifetime with. if I were you I would take into consideration your sister's opinion, that is, unless you have a relationship which would give her reason to have an ulterior motive, if you believe she is speaking from the heart and cares for your well being genuinely, most likely she sees something going on that you cant' admit to yet.

Also you repeated more than once the lack of violence, as if you need to justfy that his anger is ok. This is a problem. It says that it is a concern for you and the way that you word it really sounds more like you're trying to convince yourself that this will "never be" violent. By asserting it here more than once not only are you justifying that his anger is that of acceptable level, but if you're supported in this thinking it helps you to gain confidence that you're right in accepting his anger.

you have to be on one side of the fence or the other. Either it is acceptable that his anger is what it is (as you seem to try to justify with the lack of violence) or you need to face the fact that even without abuse or violence it is affecting your relationship very negatively.

You can't change him. You can communicate with him, but go beyond the follow up apologies from him and make him aware of the negativity he is causing. He will not do anything unless he cares for you enough to listen to this. This is the test of whether or not he is worth of being your lifetime mate. If he isn't willing to change, he's more committed to his ways than he is of being with you.