Because you are desperate, and he's an asshole. 

All of your comments and this post SCREAM desperation because you WANT him to treat you better and stop fucking around with the ex's. But hes never going to do that. So you invent the story you like in your head and that's the reality you choose to believe. 

The facts are that NONE of this is a healthy relationship and you are actively enabling the toxic behavior by refusing to have some self respect and stand up for yourself. 

You said he just turned 30. From your post I assumed you were maybe 16 at the oldest. This behavior is childish as hell and unbecoming of a fully grown adult human. 

If this is the way you want to live then by all means you are free to do so. But understand you are an active participant in your own unhappy relationship and this situation with him is never going to improve or change.