Not all apologies are innocent. Some are very harmful and can ruin your relationship. Here what you should never say:

I feel so sorry, but…

The ‘but’ part of the sentence contradicts the first part of your phrase. It mainly means that although you feel sorry, you still believe that your partner is the one to be blamed for what has happened. It also means that you know that the person is wrong and that it all depended on him. Refrain from using this apology ever again.

What a pity that you feel that way

We think this phrase is not appropriate. It makes the other person think that you do not want to be involved in the problem. Such words make you sound someone who is not able or willing to help out. Be sincere and tell your partner that what you did or said was for some certain reason and the way he feels now is his reaction to your action.