Since Oscar Isaac teased that there’ll be a love triangle between Marc, Layla, and Steven, this is how I imagine it’ll play out:
Layla and Marc Spector must’ve had some previous, established relationship. Maybe they were lovers or maybe they were married. But at some point, after Marc became Moon Knight, he entered his “Matt Murdock in season 3″ phase. He began pushing people away because he had to focus on being Moon Knight full-time. I can back this up a little since Oscar Isaac said that Marc is supposed to be a jerk who keeps pushing people away.
So Marc pushes his wife/girlfriend away, hence why he hasn’t responded to Layla’s calls and texts for months. She still loves the man, but it’s clear their relationship is permanently damaged.
Steven has Marc’s “face”, but he’s nothing like Marc. He’s timid, dorky, and really awkward. Since Steven wants somebody to love (his introduction song was literally about him wanting to be in love), he falls for Layla almost immediately. Why? Because she’s strong, beautiful, courageous, and really cool. But Steven feels that Layla wouldn’t want to be with someone like him, especially since he has this cool, badass alter who he shares his body with.
But as the series goes on, we see that Layla starts to fall for Steven...because he’s NOT Marc. Unlike Marc, he’s emotionally available, he’s kind, he’s empathetic, he listens to her, and he cares about her. They may even have things in common, like being a vegan.
So we end up with this sticky situation:
1) Marc and Layla were together, but Marc messed it up because he’s in his Netflix Marvel-phase of being a vigilante.
2) Steven falls in love with Layla, but thinks that he has no chance with her, especially since Layla was with his alter.
3) Layla is conflicted because even though she was with Marc, she’s falling in love with Steven because he’s Marc’s complete opposite.