The Line Between "Bigger Person" and "Doormat"

Question...where do you draw the line between being the bigger person and being a doormat? This question comes from a conversation I had yesterday with a relative. We were talking about my current relationship situation. In my relationship I felt that I was becoming a doormat. In my attempts to keep peace I would simply let things go. Whenever there was an "issue" I was always the one to forgive and accept. The dynamics were far from 50/50. The person I was dealing with then in my opinion took things way too far. Since that time I've chosen to take a very firm stance regarding how I feel and what I'm not going to deal with. My relative however feels that I'm being stubborn and "stooping to his level".
She used herself and her marriage as an example. Now I think her husband can be mean and stubborn and really takes her for granted. I in no way question how much he loves her and I know that he has times where he can be very sweet, but overall he doesn't give her the level of kindness and respect she should get. She on the other hand caters to him. She calls it "killing him with kindness". She proceeded to lecture me for 45 minutes on how you must do this, especially with men who are difficult and "don't always know how to show love". I do agree that kindness is a very helpful tool in dealing with difficult people, however, I am past the point of constantly bending for a person that does not reciprocate or at the very least show some appreciation for me. I consider this being a doormat.
Maybe she has taken this stance because she's already married so she feels she's stuck. But I believe that at some point you have to demand the level of respect you want and if the person is unwilling to give it to you then the person simply risks losing you. Although this stance can sometimes hurt, I believe it to be far better than the alternative of always being a doormat (which will hurt a lot more and a lot longer if you ask me). So I ask you am I wrong, should I continue catering to someone that clearly takes me for granted or am I right to be firm and stand up for myself?