Firstly this is a hypothetical question, the background first:
I have a very close male friend, we're both single so no issues. We have an emotionally intimate relationship, we spend quality time together, we confide in each other, we message regularly and we exchange hugs and kisses emojis. In person we only ever hug hello and goodbye (no other physical intimacy). We've joked about being in a 'platonic relationship' and we both date other people. Neither of us have been in a relationship since we became friends (a couple of years). And no that's not related to us being friends, we've just not met anyone we want to be in a relationship with (and no, we don't want to be in a relationship with each other).
So here's the question. Yesterday we were having a discussion about when one of us meets someone else and I said, that our friendship will in all likelihood be a problem for a new partner of his. He vehemently denies this and says "it'll be a non negotiable and if she doesn't accept my pre existing friendships and trust me on that it'll never work". I said it's not about the friendship itself, but the depth of the friendship and how much emotional energy you give it that would be a problem. He said, "I have enough emotional energy for both".
How would you feel? (..and the fact that we aren't in a relationship with each other isn't the discussion point here).
YABU - an emotionally intimate friendship with a man who is in a relationship is always an EA
YANBU - if the friendship precedes the relationship I wouldn't consider it an EA