I know you are upset, but i will give it to you straight as sometimes that is the only way.
Ok... crying to a guy because he is spending time with his mates...is not a good look. It has controlling and manipulation all over it. Also an adult having a tantrum because she is not getting her own way is also not a turn on to a guy!!! Ummm no wonder he prefers to be with his mates, than his girlfriend that is going to ball and cry over the phone at him and give him a hard time. I mean which are you going to choose!!!
He should be able to spend time with his mates guilt free. In saying that, either he could give you the option of coming with him, that way his mates get use to you both being a couple and are in it together or giving you the option to spend time with your mates and go and have a nice time out. You need to have one discussion with your man... not a week long series of nagging discussions.... you need to sit him down and and tell him you wish to discuss this and how can both of you get a solution that satisfies both of you out of it. Because clearly you are not happy with the way things are at the moment and it is only going to make his life more miserable you being upset at him all the time unless you can both come to some form of cooperation together. Maybe you should invite his mates and him around to your place or organise a few outings and ask him to invite his mates. That way he will think you are interested in him more as his mates are a part of who he is.
If he carries on and leaves you either stranded out on town to go off with mates, or does things like not turn up to pick you up or turns up late all the time. Trade him in... he doesnt like you enough and you are worth more than that. I would also look at changing your attitutude, be happy and sexy and yourself when you are around him and he might want to start spending time with you more. Cuz you know what they say..... us girls have one thing that his mates cant give him!!