linking multiple node types to each other
Okay, I haven't test this out, but I think this should work:


You first need  a way to generate a taxonomy term for each Complaint node. I think that the NAT could help with that or through Rules.
Next, add a term reference field for Solutions, enable multiple selections but disable the ability to create terms.
Override the term reference view for that particular vocabulary through a custom url using Pathauto, this would be the "Complaint1 -> Solution1, Solution2, Solution3" part
For "Solution 1 is linked to Complaint1, Complaint2, Complaint3", you already have links to the taxonomy term simply by displaying the field in your node. You could also do this through views.


Done! Hope it works!