Why doesn't my boyfriend invite me out to events with his friends?

I have been dating my boyfriend for 5 months, and I was seeing him exclusively for 6 months previous to us becoming established. When I first met him he told me straight out that he was not looking for a relationship, and so we remained exclusive "friends with benefits" until he decided to ask me to be his girlfriend. The problem is, since we started becoming intimate 11 months ago, he has yet to ask me to join him in attending any of his friend's birthdays/parties/weddings; and there are a lot of them. Whenever I have an event to attend, he automatically checks his own schedule to see if he is available to attend. However, when he informs me of a party/event he has been invited to he never asks me whether or not I would like to join him. The only exception being the first time I met his entire family during his grandparent's anniversary, which was a huge step for him. I almost forgot to mention that before I met my boyfriend he was a commitaphobe of the highest caliber. He also had many other "friends with benefits" that he kept around and has a large number of ex girlfriends. I have met his close friends on many occasions at his workplace or at his house, and we get along. I thought maybe he didn't invite me because there would be no other girls, but when he tells me about his night, he mentions other girls. He also tells me stories about previous events/parties where he invited other girls to go with him as dates, even though he was only friends with those girls at the time. So why not me?!?! I don't understand it. He tells me that there are some of his friends that he would not introduce me to (he is black and grew up in a rough neighborhood and I am Asian and grew up in the suburbs) because he doesn't want me to feel uncomfortable, but his best friend's (whom I've met and hung out with on multiple occasions) birthday is next week and again he didn't invite me. When I asked him why he didn't, he accused me of making him feel guilty for not wanting to be together all the time, and claims he didn't even notice, then changed the subject. I can understand if he wants his space, but I wonder if that is the only reason? Everything else in our relationship is amazing and progressively deepening all the time, but I can't help being bothered by this. Any feedback would be appreciate, thanks in advance for your time!