To be honest, I've never felt that. I felt like maybe as well as being his assistant, Teddy was also a huge fan of Hagen. His respect for him, as well as his pity for how Hagen has spiralled is what I pick up from him. It's like a friendship that's devolved to be completely one-sided from a friend who's been there through the years, through the thick and thin. It's essentially a case of watching his friend dealing with addiction, and sinking lower and lower in his self-destruction, and into a life of crime.
I agree that there doesn't seem to be anything with Selina and Maven either.
If you compare it to Harley and Ivy, they're a lot more overt with their references to their relationship, so I never would have thought that Matt and Teddy were involved with each other.