A. If you break up with your partner because of that, you might later regret ruining that relationship.
B. If you blame yourself then your only lowering your self-confidence which doesn't help at all with your situation. And may make the other person feel guilty.
C. If you confess how you fell and that u want to stop, makes you a mature responsible person and it also helps to be honest.
D. Blaming your partner for not being more attractive doesn't even make any sense but if it does to someone that is not the answer because you can lower their self-confidence and seriously hurt their feelings.
So, through analyzing the options, you can then see that clearly answer C is the correct one, State clearly and directly that you want to stop but maybe not so harsh and mean when you say it.