Until you can let go of this man it is going to be and always will be a never ending story and he comes back because he knows you let him come back when he wants to see you, the only way you are going to get over this is to stop all contact and not allow him to enter your life and then leave whenever he wants to. If after all of this time he still doesn't have feelings for you he probably never will and as hard as it may be to face the fact that he may never have feelings for you and treat you like a girlfriend. The reason you find yourself calling him and again and wanting to be with him is because you haven't found closure in the relationship and you're always wonder what if things would change or will he finally get feelings for me this time. You have to realize that you deserve better than what Marcel is giving you and that you shouldn't be used in that way. He will only do what you allow him to do to you so it's time for you to make yourself strong enough to let him go and find someone that respects and loves and cares for you and takes into consideration your feelings.
No matter how much you may want to be with him if he doesn't want a relationship with you he will not be there for you the way you want him to be. You may have sabotaged the other relationships because they were not Marcel and didn't fulfill your needs the way that Marcel could but as long as he does not want a relationship with you it will always be you sitting there wondering why he won't commit to you or why you can't make him love you. You may want to consider counseling also they can help you to find way to occupy your time so that you are not wanting to be with him like hobbies, volunteering things that you can do to get your mind off of Marcel so that it will be easier to find closure and move on from this unhealthy relationship.