I F37 slept with a long time friend M35

For context, we grew up together have known each other around 28 years, we were always with his younger brother M34 and all had a pretty strong bond, I moved away for 13 years with my previous long term partner of 16 years and returned to the UK 18 months ago after separation. One night a few months ago he gave me a lift home and things got a little heated between us. we spoke a few times in the following months and everything from my perspective was fine. communication then dwindled on both parts since then silence. My “friend” is now in a relationship.

I have now started to get dirty looks off the brother (also in a relationship) socials have been muted and some removed, no conversation and there clearly is a toxic bad vibe when he is around.

I’m completely bewildered at what I have done. is this just the now mannerisms of men in the UK? Or I’m I now more accustomed to men actually having the balls to communicate and having some level of manners and respect. Am I missing something? Or just being naive that two people who had a great connection can still be friends after sleeping with each other and with their family? Would love to get a mans opinion on this