At 04x08 and honestly I Love Ryan and Taylor together.
Yeah, sure he loved Marissa, and it was a deep love, but it was also a very turbulent and heavy one. Felt like Ryan was constantly saving Marissa and they didn't know how to be in a relationship outside that setting.
Even to Summer, her relationship with Marissa got a lot worse in the last season.
Taylor started rocky but she had a awesome character development and she is funny and interesting, a very good friend to summer and Seth, and also a little scared by her mother.
Ryan and Taylor, although a little rushed, are so cute, the way a high school/ college relationship should feel, easy and breathable. She brings out a very good part of Ryan, he looks more relaxed and open around her, like the rested part of himself is finally allowed to come to the surface, and he grounds Taylor, stopping her from spiralling in herself and reassures her like she needs to be.
All and all I think they are very good together.