In synastry, situations like that tend to happen when there's some heavy Saturn and Pluto action going on, which you have.Saturn has a hard time letting go, and Pluto tends to be obsessive.
Nodes definitely add to it - making it seem like it's fated and supposed to be..
Thing is, just because you want to be with a person, doesn't mean you will be.
It's sad but a lot of us go through things like that - you're into someone but just can't be with them.
Don't ask me what the purpose of such connections is, it may be karma, a lesson, whatever.
Thing is - you have to live your life, and try to be as happy as possible.
If a certain person cannot give you that happiness, force yourself to move on and don't look back.
Get them out of your system and look for someone that CAN make you happy and WILL try their best to make you happy.
You deserve it.
Don't waste your time!
Best of luck ~