While I'm no expert, I definitely can voice a few facts:
You decide your life, and if a relationship doesn't turn out as expected, then it's not just your fault. Considering what the other partner is like, the reason for a breakup can depend on a whole lot of variables.
If the partner is a 'toxic' person, then you definitely need to understand that continuing a relationship with that person, will only do you more harm. In such a situation, it might be hard to make a final decision, but it should be understood that making the decision will definitely free you from the unwanted relationship in which you are in.
I remember having a friend like that - not a relationship, but just friends. And the whole 'friendship - thing' caused a lot of stress and anger to build up inside me. And I eventually had the opportunity to stand up against this particular 'friend'. From experience, I'd really like to say, that while hurting other's feelings might seem like a very hard option at first, you should be able to 'weigh' the amount of times you've been 'used' or exploited by the other person. The amount of times you've felt guilty of being yourself, when you were with that person.
Because if I were to continually worry about hurting the other person's feelings(by breaking up with him/her), and only view it from their perspective, then I'm bound to get myself into more emotional conflicts inside myself. Sometimes, you need to look at yourself as well. I don't think of it as being selfish. Especially when you're the person who is suffering from all the emotional stress - and that too, when the other person seems blind to the problems you're obviously facing.
This is just a single point of view, and it doesn't have to be this way for every relationship. I'm sure you'll figure it out yourself eventually :thumbup: