Basically agree with everything you've said here. It's true there is dysfunction in their relationship but at the same time their love for each other is immense. I read a fic once which had a line that said something to the effect of, their love was so big neither knew what to do with it. I thought that summed them up pretty well because you had two messed kids, madly in love with each other, repeatedly placed in impossible predicaments. Ultimately, I think their relationship could have gone either way, they fail or they succeed. But I've always preferred the idea that they both overcome their individual problems and eventually find themselves in a position where they can make it work.

RE: Ryan/Theresa, I don't think it was love. Maybe a platonic kind of love but Marissa was definitely imo his first love in a romantic sense. I think that's how it comes across in 1.14, if Ryan had already been in love before, I don't think he would be as unnerved as he was in that episode.

And the whole baby issue is kind of a mess. They hinted pretty strongly it was Ryan's and then revealed it wasn't in season 3, pretty obviously for the sake of convenience. Tbh it is just easier to think that the baby was not Ryan's.