<human>: Can you condense the text into three sentences or less?

So my fiance and I have been engaged for about 6 months now, living together for a year, been dating for almost 3 years. We first started dating about a year after I broke up with my long time girlfriend of 5 years who I never really got over. After that break up I chose to become a very emotionally distant and cold person on the inside but very happy and all around nice guy on the outside. Which has brought me to my current issue. I thought that I would eventually be able to move on past my old relationship, cut off contact, deleted all pornography, etc... but unfortunately I have not been able to despite everything that I've done. 

I've talk to my fiance about that several times about how I feel and she has been very supportive but I can't help but feel that I am not ready for marriage and would like to break up with her. She really deserves someone who will be able to reciprocate the love that she has for me. I've talked with her about ending our relationship in a calm manner and it usually leads to her crying and begging me not to leave her but I am not happy despite there being absolutely nothing wrong with this relationship. 

I've gone to speak to a professional about this and have been diagnosed with depression and they have recommended that I end the relationship as it is probably not the best idea to be in one in this current state of mine. I'm just not sure how to end this, everytime I've brought it up it ends with me staying and being miserable. I just don't know what to do anymore. I'm fairly confident in saying that this will lead to a failed marriage if we get married.
<bot>: Broke up with ex, dated another girl a year after, didn't get over ex, got engaged, tried breaking up, still together and miserable and not sure what to do.