Please help, what should I say to my boyfriend

So I have been with my boyfriend for 3 and a half years, since I was 15, and I am now 19, when we first began dating, he did not have a lot of friends, so he hung out with me and my friends a lot, and this never bothered me because I wanted to make sure he was having fun and not sitting alone at home all the time. When we were about 16, he started to chum with some old buds of his from elementary school! I was happy of course that he had finally found some friends and I didnt have to worry about always including him with mine, but of course once and a while I loved to have him a long. Now, however, when he had his new friends, I was never ever included when they hungout, now I am totally 100% respectful of guy time, and having guys nights and not intruding on them, but Im talking, when the other girlfriends of his friends were invited, I was not. And this has happened repeatedly over the years, and after all this time I can probably count the number of times on my hands ive been out with him and his friends...Now that we are over 18, hes started going to the bar with his friends. I didnt mind that they all went together as a group of guys, but after discovering on facebook that it was never just always the guys, that the girlfriends of the group were also included and not me.. I was really hurt. We got into big arguments about how I am never invited and why he chooses to leave me out and never include me. He will come up with numerous excuses, like his phone died, and couldnt call me and his friends wouldnt let him use their phone, or he had no idea anybody was bringing their gfs, or assumed I wouldnt want to go, its ridiculous how many there are. Now Whenever I go to the bar with my girlfriends, I always try to include him and his friends, always! I will try and arrange that him and his friends all come with mine and we have a night together seeing as he never makes the move to plan it, or invite me... but however this never seems to work as his friends wont come. Just the other da he told me he was thinking of going out to the bar lastnight with his friends, and me being frustrated about never being invited or hanging out with them when their gfs get too, I said ok, well maybe I could come along and bring some of my friends, and he sorta just said.. ohh.. yaa not wanting to.. so after a talk I gave him about never being invited along and how it would mean a lot to me if we finally all went out together, last night he texted me saying oh were not going to a bar, and I replied saying thats ok, me and my friends are looking for something to do, wanna meet up, and thats the last I heard from him all night, I got home to discover a photo on ffacebook of him and his friends at a lounge by our area, with the other girlfriends invited. Of course his phone was dead so Im sure that is going to be his next excuse as to why , yet again I was not included. Can some one please help me try and figure out why this is happening and just what is the right thing to say to him, to get through his mind!