Marco looked with a loving look in Yelena's eyes there was no hint of insanity when he transferred his emotions toward her, in a bandwidth and capacity that words could not possibly express. He was with her, she was the most significant person in his life, and despite his pain she was always in his mind.
Marco has lowered his defenses, he lowered them in order to love again. However, these were the same barriers that have kept him sane all these years. They blocked external influences on his mind, but have crippled him. Marco has made himself a blind mage - because he needed to survive. He was too sensitive, and he could not withstand the way his emotions manifested themselves in the astral world. Everywhere he went there were evil daemons telling him things about people, things he did not want to hear. Telling him that these people are not Christians - that they are murderers and that they could not possibly be real priests.
But how can you accept that everything you know - every single thing is a manipulation? No feeling is authentic - that you are slowly being programmed to be a doubtless killer. Controlled by religious emotions that are not shared by your instructors. That their religious teachings are not sincere - this is after all your entire world - there is no family, no love nothing to lean on. So Marco has built a wall, a great wall preventing him to observe the fallacy of his world - a wall that made him immune to mental manipulations - at least for a while. That wall has also made him numb, his magical talent disappeared he was unable to learn new magical skills. His astral access disappeared - he became the first mage that could not observe what he is actually doing. From a young prodigy he became last in his class - but he was not programmed to be a killer.
That was something...
Why was Marco sent to Seattle? He was sent to Seattle in order to fall in love. Because his instructors knew, that once he allows himself to be vulnerable their education would kick in. That he would be in so much pain, so much guilt that he would beg them to make it stop. He would litterally return to the Vatican to beg Gabriel for a confession, he would be back because he needs that confession like a junkie needs his next fix. It is only when Marco is truly broken - only when he say that he would do ANYTHING for a confession - only then he would be ready to take life.
"Yelena, the control of the Vatican on me is far greater than I ever imagined, they brought me here to fall in love. To allow my mind to be vulnerable, all my life they have poisoned my mind but I blocked them. I buried my emotions deep inside, I berried my magic inside my own astral senses. Then I came to Seattle - no strings attached, just as they told me to, and slowly bit after bit I begun to feel again. I begun to care, I learned more spells in this year on my own than I did in an entire life with access to the best teachers, to an endless wealth of knowledge.
It was your love that doomed me. I finally gave up my barriers and as I did all their poison was free to infect me. My guilt causes me physical pain, I am a prisoner of my own emotions and my logic is not strong enough to defeat these emotions. There is no hope for that, I was programmed to be controlled like that since I was very young. I was never free.
My path ends in one of two ways, either I return to Italy and beg for a confession. I tell Gabriel that I would do absolutely anything if he can take away the pain that I feel, that awful guilt. The devil always win, I can never be good.
The only way I could possibly deny the devil this victory is to take my own life, I am committed until death, then I am free. Even if I go to hell I do not care, I never want to kill for them. Please, help me do that, give me the strength to die like a decent man rather than live as an emotionally crippled assassin that kills and then begs for forgiveness, kills and confesses. Allow me to die the man you love rather than to live like a monster."