I'm sorry superman, but I have to agree with these guys...
I don't want to make you feel bad, and I want you to know that I KNOW you love and care about your son, but I think that sometimes your priorities involving him are a little out of line. I'm just so worried for you, because you have to stop this stuff or else his mom is going to have all the dirt she needs on you to get full custody. Never seeing his dad would be terrible and hurtful for James, and I hate to think how much it would just kill you too if that happened. I see it happen all the time, PLEASE don't let it happen to you.
Sometimes you have to kiss up to people for the benefit of your son... come on, its not that big of a deal. You don't have to live with his mom or date her and make her happy that amount of time. Just fake a smile and some politeness when you DO have to see her and maybe things wouldn't be so bad? I'm sure you had to do or say something kind of obvious for her to get upset or assume you were under the influence, you know? You don't just pretend like someone is high to strike up a fight...
Also, she may have felt safer by sending out her boyfriend to ask you to leave... I'm not saying it was appropriate, and maybe she stepped over her bounds a little bit, but it sounds a bit like you were flipping out and causing a scene, so I guess its either that or the cops? You know? And NO, he NOT replacing you, you will always be James' dad so don't think like that it will just drive you nuts, BUT if you keep up acting like this, and she gets full custody, then maybe he will replace you.
Do you want that to happen?
Think of it this way. Do you know that if she breaks the custody agreement, you can go down to your local authorities and literally have them come over and force her to hold up her end by sending him with you? I have seen it done, its not a court order for no reason. It is upheld by the law. BUT my question to you is, do you feel like you were in the right position to go to the cops? Would you go? Or would you be too worried that she had the right story? Or that they would test you to see if you were high/drunk? That maybe it would be more trouble for YOU then it would for HER if you went to the cops? Well if the answer is yes to any of those questions, then you were in the wrong and she had every right to keep him from going with you because it is her job and instinct to protect her child, as his mother. You wouldn't protect James from a bad situation if you knew you could? I know you would.
You gotta think things through, don't just get angry and flip out. If you know you're getting James on a certain day, don't smoke or drink at all that day, come on. I've been around pot my fair share, and I don't believe you are 100% sober after an hour and a half of not smoking, after smoking "throughout the day". At least, not sober ENOUGH. Know what I mean?
I know you're mad. But you have to think about this stuff.