You can request a new court appointed attorney but you will not be given one. If you want a different lawyer, you will have to hire one to substitute in for you.
Contrary to your assertion that the lawyer had nothing to do with pretrial diversion, you are wrong and you were lucky to have received it. Had you completed it, then the case would have been dismissed and you could have removed it completely from your record. Now, your choices are going to be far more limited.
You will have a right to a trial - jury or judge, or a right to plead guilty to the charge. The State may or may not offer you deferred adjudication or straight probation and even if they do, your failure to succeed on the PTD indicates that you would not be successful on either type of probation. Many prosecutors will not offer any type of probation after PTD has been violated. Moreover, some judges, even if the person is offered probation, will not accept the plea given the offender's unsuccessful history on the PTD. As far as joining the military, while that was a bargaining tool years ago, most prosecutors will no longer offer to drop the case in exchange for enlistment - and especially in your situation where you failed to keep your side of your contract with them on the PTD.
Deferred and straight probation are very, very similar to PTD. They generally are a little less onerous but they have meetings and other requirements, too. In addition, unlike PTD which has no court costs or fine, there are court costs and fines associated with probation. Unlike PTD though, they will remain on your record forever.
If you receive deferred and successfully complete it, you will be able to apply to seal your record 5 years after successful completion but it will still be on your record and accessible to many. If you get straight probation, it is a final conviction. The other choice is prison.
You should have listened to your lawyer and put the PTD first on your plate of priorities because you will have to suffer the consequences of your choices now forever when you had the opportunity to "fix" what you had done wrong. Your lawyer is probably right - there probably won't be more deals until you are indicted and the deals are not going to be near as good as the PTD you messed up.
As stated in the prior answer, things have changed as far as going into the military to avoid criminal problems. As a matter of fact, with the economy there are so many people attempting to enlist. There are often LONG wait lists to get in depending on your job, and they are not messing around with anyone that shows they might be a "problem." With the numbers and quality of people attempting to enlist, the military is able to be very picky about who they accept.
Have you talked to a recruiter yet? If you are serious about your future, I urge you to take action on your own to talk to a recruiter. They will be able to tell you what you would have to do to qualify for the military, and you will need them to get involved. Usually, the prosecutor will want to know that you have already done EVERYTHING you need to do to be accepted into the military BEFORE they will even consider the option.
But again, like the prior post stated, you may have already lost your chance by not completing the Pretrial program.