I’m looking for clarification regarding combat space in a one-on-one combat situation, since it impacts disadvantage rolls and opportunity attacks.
If a medium size opponent attacks you with a melee weapon (one that does not increase reach), it’s assumed they are within 5′ of you (PHB 146). Based on the “SPACE” section in PHB 191-2, they are in one of 8 squares bordering yours. Regardless of whether it’s a hit or miss, it’s now your turn.
You’re a spell caster that only has an option of a ranged spell. Let’s assume you have no ‘touch’ spells and no melee weapon. Based on PHB 195, would you have disadvantage on your ranged spell attack roll because you’re within 5′? Or because each creature is in its own 5′ space, there is really 10′ between them combined, so there would be no disadvantage roll on the ranged spell attack?