I got the gist of Restart but I didn't feel sad while reading it. I think I missed somethi...

I got a little confused too?
This is how I took it: Miki and that guy hook up, and Miki keeps making out as if it's just a fling sort of thing, but in reality he actually really really liked white hair guy (whatever his name), and was more serious about him than he was letting on. Eventually Miki and white haired guy (let's call him WHG) watch the news of gay marriage being legal, and Miki "jokes" about how they should get married. WHG responds like "this is just fling thing though right?" And then questions Miki's desire to actually settle down and have a family.

Which Miki does want. Thing is, he seems to express desire in wanting to bear the child, be a mother. I don't know if if this is because he wants to be a woman or if he just wishes he can bear children, but the question upsets Miki since he obviously cannot do so (thus why he looks sad and says "have kids...something like that..). He ends up going to Thailand and during speaking to one of the ladyboys there, expresses his desire to turn into a woman. The ladyboy reminds him even if he has surgery to become a woman, he will never be able to bear children. This upsets A drink Miki, and he wonders outside and has an accident.

The accident leads him to have "a few screws loose". He acts and says all the things he truly wanted to before in a child like manner (the "before" Miki always put on a face and pretended, like how he pretended his feelings for WHG were nothing serious). He now says I Love you to WHG, and wants him to "cum inside" because that's his desire to want to have children.

But of course Miki will never be able to bear children, nor will he ever be "normal" again. But he and WHG end up happy together.

Now this could be HORRIBLY wrong since I got SO confused lol

That was also how I understood it! But I don't know I really feel like I missed something? I didn't feel any sadness while reading it dafuck, others did, I feel so unsatisfied dafuck. HAHA

The writing style just left me a little fuddled; it didn't really flow right, so the emotional impact was a bit sabotaged for me aha but I loved the art, and thought it was sad how he desperate he was to want to have children but couldn't :/ I just wish it flowed a little better

? For me it flowed perfectly! all the little details, the things left untold, just little glimpses letting reader build the understanding of charactrer. I like it much better than flat on the table explanations that dont live place imagination

Maybe it's just a matter of preference for the paneling and plotline flow, it's good to leave the small details untold but to keep them sealed in one place and suddenly unraveling all of it without any proper transition kinda messes up the timeline and flow of the story? Well, that's how it appeared to me.

What I understood was,
Miki wanted to try same sex relationship with white haired (W) , then he liked it , and he was just emphasised it was flying because that time gay was treated disgusting. Both actually liked eachother, when the same sex marriage law came , Miku was pretty excited , so he suggested marriage, but W thought if he agree , Miki will just make fun of it , like he always do , so he said we both want normal family right? , but Miku was pretty hurt by it, so he went to Thailand to change gender so he can bear children for W , but when he got to know it's impossible, he got into accident, as he was pretty shocked or something he lost his memory, it was kind of trauma response, but he became honest after it