As a side note, it slightly bothers me that they use the Lemegeton and a limit of 72 demons, and many characters have the right names, yet he contracts right away with Carmilla and later with someone named Thor. It's fine if their original name isn't a Goethia demon to keep the reader from automatically knowing the character will be a comrade, but they could have had a different name for the avatar he summons, and it's kind of sad that he will never be able to collect all 72 of the original demons.

after ge defeated the hero and friend, he meet again with the Hero and friend outside and BAMMMM!!! he reveal that he is the demon lord hha! MOTEOVER WITH ALL OF HIS OTHER DEMON FRIENDS (FLOOR BOSS) HAHAHHAA!

If you read this for romance, get out of here. The MC trains so hard on his childhood that he don't have times on things like this. He didn't even have time to go to school and learn youth. Fenix and him also started as a party even when their young. So you shouldn't expect the MC to act like gigolo or proactive in romance.
Now calling the MC so dense is wrong. First he knows how Milia felt about him. It seems like he's taking it slow, but it's not like he doesn't acts. Of course it's not so much, but as of chapter 226, there are romantic moments, also you'll notice that along the way, Milia became an important person to the MC. Sometimes they unknowingly flirt while in front of their friends and the MC just blush whenever he take an action. In the first place, as of chapter 226, we're just in the fourth arc if I'm not mistaken, so you might think that the progress is just too slow, but it's technically not.

The MC is hiding his powers, because it's too strong, came from the former demon lord, which may brand him as heretic. He also promised his master to don't used it, unless it came to the point that there's something happened that he have to break the promise. The reason he didn't defend himself are a lot. Like how his team is not growing well because of his supports, or how he didn't feel suited in their party.

Not really. The vampire lady Milia, force herself on the MC, and the MC just feel troubled. If he accepted her immediately you can call it forced. But he didn't instead over the story, he is learning to love her. So it's just a force start but not a force romance

This is entirely wrong, throughout the story you will learn why he left and how it's their both (him and his party) fault. Also they already make peace.

Did this guy read the synopsis. The world is at peace. Dungeon crawling become a piece of entertainment, but it's not a happy go lucky professions. The skills of adventurers are real, same with their strong motivations and what should the heroes do? In the first place not all heroes are adventurer same with other people with combat jobs. Some are on knight order which now acts like a security and there are persons that's not interested in dungeons.
Black and white? Heck, you can say the all characters here are white. It's a peaceful world with wholesome interactions so it's just right.

The heck? Characters here are so interesting and have a their own motivation and aspiration. If you read only up to volume 1 which is around ch 50 then you don't know much of the characters. In the following arcs we will see how those characters shine in their own way.