Passive-aggressive relationships are characterised by one person attempting to assert control over the other while avoiding open conflict. While on the surface passive-aggressive people will appear friendly and cooperative, they will covertly try to sabotage and control various situations. Everyone acts "passive aggressive" at times; the problem occurs when this becomes the go-to coping mechanism for anger. When confronted, the passive-aggressive person will typically feign ignorance and act hurt. Therefore, ending a friendship with a passive-aggressive person can be especially difficult.
Recognise a passive-aggressive person for what he is. This can be difficult because many passive-aggressive people are particularly good at masking their negativity. For instance, if you ask a passive-aggressive person to do you a favour, and he really doesn't want to do it, he will agree to anyway. However, when it comes to actually doing it, he will show up late, say he'd forgotten or have a pressing matter to attend to. It's important that you don't take these events at face value and, if they persist, recognise the person for what he is.
Confront him. You must do this if your friend's passive-aggressive behaviour is ruining your relationship. This will be difficult given the conflict-avoiding nature of passive-aggressive people; expect a lot of theatrics, up to and including fake tears. It's important that you remain calm during this encounter because your friend will want you to lash out at him, thus legitimising his response. Planning out your grievances beforehand will help you calmly lay them out.
Stay on point and make your case. During this confrontation do not engage your friend in hairsplitting regarding specific events. Remember, passive-aggressive people are master manipulators. They will attempt to break down your case using a series of excuses that shifts the blame from themselves and obfuscates the issue. It should also be noted that confronting your friend will most likely not fix the underlying problems that cause the passive-aggressive behaviour. In any case, it's cathartic to at least air your grievances.
Cut your friend loose. If this confrontation fails to fix the friendship, your only course of action is to end it. Ultimately, a friendship is only worth maintaining if it contributes to your happiness. Once you make this decision, you must remain firm and cut off all contact. It is useful to formally announce this via a one-way message to avoid argument.
Most likely your friend will try to spin events to look as if you're unfairly abandoning him or have somehow caused the conflict. He may try to use your mutual friends to his advantage, and try to lobby them to his side of the issue. Ignore this; engaging with him at this petty level is what he ultimately wants. Discuss the situation with your mutual friends and let them know why you're ending the friendship with him; emphasise that the conflict is between only you and your ex-friend.