Boyfriend is too close to his female friends?

So I (29) have been with my boyfriend for 3 years now and he is a university student, he recently met two girls in one of his courses and became good friends with them, I'd say basically bffs.

At first I didn't have a problem with this until I found out that their friendship is very intense, they meet twice a week talk everyday about 5 times a day in their group chat and also in private messages specifically one girl.

one of the girls has a boyfriend so she does other things and has a life but the other girl is single and is not doing so well in the dating life so she seeks emotional support from my boyfriend and talks to him about everything, basically getting all the benefits of a relationship but without sex. I was very uncomfortable with this because I am pretty sure she is interested in him, I found 50 love notes in his room from this girl and when I asked about it he said that she made those for him because they did not meet for three months and she missed him. correct me if I'm wrong but this is not a good friendship its beyond that, she also talks to him about sex whether if its sex jokes or her planning to have sex with guys she is dating she will tell him about it but I thought I would be controlling if I ban them from being friends, until I asked him a random question if we were not together would you have sex with your female friends and he said he would have sex with that one friend that is single and when i asked him if he finds her attractive he said no he just thinks she is good looking. so at that point I banned him from being friends with her because I felt uncomfortable however, I feel really bad because he is very sad this has happened and i just wanted to ask am I wrong for doing this? what other solutions are there and is this normal for good friends to be like this?

There are many other things she did that I did not like but i tried to make this short.
Boyfriend is too close to his female friends?
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