If something is broken it will never work like it use to. You may think that it is still good but now that is broken it is not doing the job the same way. It is important that your retainer is not broken and that it is replaced. By wearing a broken retainer it will not be able to do the job required in order to fix your teeth.
By the way you worded your question I am guessing that you are a minor who is concern with what her parents are going to say. Try thinking about it this way. True your parents may get upset about you braking your retainer. However, dont’t you think they are going to be even more so when they find out that not only did you brake your retainer but that you broke it months ago and did not tell them. You are lucky that you have parents that not only can afford to get braces for you, but care about you enough to make sure you have braces. So be fair to them and let them know what is going on.
This is one suggestion: Tell them right way what you did. Hopefully they have insurance that will help with the cost of a replacement retainer.
Second own up to what you did and offer to take responsibly for it by paying it off. You can do this by getting a job or by working and doing chores for your parents. Taking responsibly for your actions will go a long why with your parents.