Gf has a Male best friend

So I(31M) am in a relationship with a girl 28F that I met on a dating site. We're in this relationship for 6 months now and while we have our share of ups and downs we are serious. We really love each other.

Now the thing is she has a male best friend. So for the first 3 months I wasn't aware of her male best friend. One weekend when we didn't meet, i had asked her about her plans for the day. She said she's going on a movie with her friend. After a few hours I texted her and came to know she went to watch back to back movies with this 'guy best friend'. They probably had dinner too. Well this kind of made me feel quite uncomfortable.

Later I discussed about boundaries and expressed how it didn't sit well with me with the fact that she's hanging out one on one with this best friend and spending time together even when I'm in this relationship. I didn't want to sound insecure or overly possessive but did ask to maintain a boundary. We agreed no one on one meets but group setting is fine.

Few months later, I got the chance to look at her WA. Reason: I earlier had confidently shown my instagram msgs and so expected the same transparency. Somewhere deep down I wanted to know whether this best friend is on her top msg list.

She wasn't at first comfortable don't know why. But I argued that if I can show what prevents her.

So indeed that best friend daily texts her. Although their exchange is short. But it involves him asking for pics whenever shes on a vacation. And she readily shares her pics. He would always asks for her status...like whether she has landed on the airport.. whether she has reached home etc. he has tried texting her after 1:00am too asking if she's awake(she wasn't). He also asked her to go on a movie with him and on other occasions too. And she was agreeable. Although that didn't happen. He texts her 'miss you' and also sends her kiss emojis.

Apparently this best friend has a gf too. Now my question is why would he want to make so many plans with my gf and not give his focus on his gf. My gf says he is just a friend and looks at him just like a bro. Why would he ask her out when she already said no one on one. I found this really upsetting and suspicious and discussed this with her

Although she seemed that I was making a big deal and it's just her friend but I mentioned that there should be a boundary. And he's crossing the line of how a good friend should be. She seemed oblivious to all of this of course. And I'm sure she feels I'm insecure.

I don't understand if I make my gf my wife why should I be comfortable letting a guy text her daily, text her at 1:00 am and allow him to ask for photos or hangouts one on one. I simply don't get it.

I really felt bad that my gf was oblivious and was agreeable to him. I felt cheated on.

Is this feeling of mine justified? She may have hanged out with before I entered the scene but I assumed with time she would slowly withdraw and set a boundary herself. And not provide the privilege or privacy of her. And make our relationship special.

Is i am wrong in thinking that way. Want your valuable advice folks. Thanks!