Welcome to the crazy world of love and romance!! I feel for you - I have serious jealousy issues too, which are really just self esteem and fear issues, and you know what they say - fear is the opposite of love. I can't say I've resolved my issues, but I'm better these days at recognising them for what they are - just fear. Same as my fear of dogs and my fear of the dark(!)... it just occurs automatically, but if you're aware of it, it doesnt run away with you as easily.
Your brain will probably always be running those ridiculous scripts... you know the ones "What if I get cheated on and made a fool of and laughed at and left all alone...", all I can tell you is that most people experience the exact same thing in relationships to some degree or another. You say that you tend to look at things from a spiritual viewpoint and that gives you an advantage that many don't have - you might find it easier then to look behind a persons behaviour and the facade they show to the outside world, to the real person inside and see the fears that might be driving that behaviour, and to see the good that's buried in there.
One more thing I'll say to you is this - I've been through a number of those nightmare scenarios that people fear in relationships, and I know this is a bit of a leap for some people to believe, but I wouldnt have it any other way. I learned things about myself that I wouldnt have otherwise, and I experienced emotions (some of them really painful) that I couldnt have experienced if every thing was all hearts and flowers all the time. You refer to getting 'no reward' (and at the risk of sounding like a masochist) I'll say that not every reward has to be pleasant.
Some of my worst fears have manifested in my relationships, and at the time I thought "See - I was right to be wary, exactly what I feared happened..." but time and experience have thought me that you attract what you give your attention to - the self fulfilling prophecy. (These days I use my powers for good ha ha) I know it's not easy, but try to keep your thoughts positive and focus on love rather than fear.