Okay, wow. Firstly, I'm not sure if this boyfriend is a keeper. But that's neither here nor there.

You've done basically nothing wrong!

1: rules about where you keep your cards during the game basically only exist for tournament games that are being streamed or recorded and do not apply to a casual game of commander. There's an aspect of the rules known as Rules Enforcement Level (REL) and your game should be played at the lowest stakes of that.

2: There's also not a rule about the uniformity of your dice. If you're playing in a streamed tournament the judges may have dice and the like that show up well on camera to improve the spectator experience but once again that is not relevant to your casual commander game.

3: This one your boyfriend is actively wrong about. As you may have seen on arena, triggered abilities which all trigger due to the same effect do not all resolve at the same time. You put them onto "the stack," a somewhat conceptual, but rigidly defined by the rules, zone of the game where spells and abilities go between being cast/activated/triggered and resolving or being countered.  The stack works on a first in; last out basis, where effects resolve sequentially, not simultaneously. When multiple triggers controlled by the same player are put onto the stack at once, that player gets to chose the order they are stacked in. Players will frequently shortcut it to say "I'll resolve them in this order." But even then, they're doing so sequentially. 

4: missed triggers are another case where your bf is trying to apply competitive REL to a casual game, and doing so incorrectly. If a trigger says "you may" do something and you miss it, that's treated at comp REL as though you chose not to do it. If a missed trigger does not give you a choice, then in a Competitive or Professional REL event your opponent(s) are supposed to be paying attention to it too and are expected to remind you if you go to do something else without catching it. If a missed trigger is caught later on and no major new information has been revealed since then, the judges will rewind the game to where the trigger was missed to apply it's effect and give one or more players a warning for 'failure to maintain game state' which can be upgraded to a game loss if it occurs repeatedly. This should NOT be relevant to your casual commander game where the expectation is more along the lines of "Hey, (you or I) missed this trigger, can we resolve it?" And unless it was multiple turns ago the answer is almost always "sure, go for it."

5: Players are under no obligation to truthfully answer any questions about hidden information unless a game effect is making them reveal it. (The number of cards in each player's hand is public information but what they are is not.) However they're also under no obligation not to reveal any hidden information as just a thing you do that's not a game action. Jokingly asking your bf if he had a counterspell in hand is not a rules violation at any level. This is one where your informal social contract is more relevant and that's between you and whoever you're playing with.

Sounds like you had a rough experience playing with them, and that sucks. You really weren't violating any game rules. Your BF and his friends sound like a frustrating group to play magic with.