Yes, the "what if's" can be a real killer, but I suppose to a degree I have started to accept that I was at least able to brighten his world for a time - be it a short time.
You would think that realisation would set in after having had so many people "discard you" but I am a stubbornly eternal optimist and I always try and see the best in people - this is where I often fall short... I think. However, on the flipside of that coin, I never want to harden my heart... but I am realising that I need to see things for what they truly are and cut my losses, as you said.