<human>: For the past three months I have been hanging out with my friend (of 8 years) and his girlfriend (of 2 years) a lot more.
 This is the first year they have lived together and she and I have been getting a long pretty well and actually becoming friends. My friends are kind of a stoner crowd (I actually introduced all of them to weed) and I have recently quit smoking weed. So I was planning to get out more and be active now that I have escaped my marijuana cocoon. In a text to my buddy's girlfriend I briefly mentioned that I was planning on hiking more and maybe going to start to explore the city around me. She got really interested as well and said she had been getting kind of depressed just sitting around the house all the time. So we made plans to go see a movie on a day my other friends were going to be at a concert neither of us wanted to attend. (plans were made and known about for a few days before said concert)  Then we hit a Saint Patrick's day Parade and had a fun time hanging out downtown eating food etc. Of course both of us know this is strictly a friendly outing.  Fast forward to last night and my buddy kinda loses his shit on me. Turns out he is upset I didn't ask permission to hang out with his girlfriend. Now this is somewhat hard for me to understand as a person who hasn't been in any serious relationships. I am thinking we are all trusting friends, they are a very established couple, why can't we be friends and hang out sometimes? He says he is fine with us being friends and hanging out but he feels completey disrespected, but I just don't see it that way. I obviously didn't mean to hurt him or upset him. It just seems bizarre and antiquated to ask permission. Why can't people be alright with opposite sex friendships without bizarre handing off rituals?

Can you succinctly summarize the text in 1-3 sentences?
<bot>: Hung out with my good friend's girlfriend downtown alone for a day (as friends) and he freaked out on me and felt that I should have asked permission.