I'm a believer, that Remus was in love with Lily, but he never told anyone about it because of James.
He wasn't dramatic about it. He didn't blushed like an idiot around her, he wasn't shy. Lily was his friend before anything and they had this brain connection between them, because they both like books and are a little nerdy. He could look at her a little too often sometimes, thinking about her in the night or drink alcohol sadly, when he realized that Lily likes James back and he's just an awful friend to have those feelings for her.
I see Remus as demiromantic, because the way he falled in love with Tonks seemed like it. And I ship him mostly with his friends xd
Sirius is the only one who knows. They never really talked about it, maybe only when Remus was drunk or out of his mind after the full moon, but in general he's just a good observer. And maybe he was a little jealous.
(Remus might or might not have a little problem with alcohol)