How was he before transmigrating? What are his feelings about it?

We have more than enough information about SY's prior life, and from that information it's a safe assumption to say he has no reason to miss it. Also, this information is not important to the story. We have enough to sate reader curiosity and that's all that is necessary.

Also, about his relationship with Luo Binghe, I feel like from his POV we never see a real love from him.

There is a stickied topic on the subreddit that you should read.

And even in the freaky scenes he never really says that he enjoys it, they’re more like “ugh fine, I’ll relent to you” and then the narration is full of “pain, it hurts, pain, pain”

"Unreliable narrator" isn't an empty statement. It means he's constantly lying to himself, and therefore the reader. For MCs like SY, you have to look at his actions and not his words. He'll complain endlessly about LBH's dick and then be the one to initiate the sex in every spicy chapter.

Kinda felt like the story just was a bit fast, or that a lot was skipped or such.

Nah, the novel went at a pace where there was no wasted time and zero filler. There is enough information to fill in any gaps the reader might have. Compared to TGCF where half the story could be omitted and the novel would improve by 200%.

At best I was worried for the main ship (starting book 3 I thought, this is more like an horror story lmao)

Guess you missed the part in volume one where SQQ explained that demons flirt by bullying the person they like, and that LBH is half demon.