What should I do??

Personally, I would tell him now, because that way he might not come looking for you when he gets out. However, if he is the jealous and/or dangerous type, I would make preparations to try to make sure that you and your new boyfriend are protected when he gets out - just to make sure neither of you gets hurt, but still tell him anyway - because that way he knows that it's over between the two of you and doesn't assume anything. However, that's just my personal opinion. Good luck anyway! :)

Tell him now and pray you never run into him. If he's understanding then everything should be fine no problems, if he's not and gets mad its better you tell him now so he has sometime to think about it. Good luck with everything.

I am sorry about your predicament. What are the chances that you will never run into him or that he will look for you? Are you still in contact with him and perhaps given him the idea that you are waiting for him? If yes then you should tell him now. I would be mad if the only thing I was clinging on to when I get was that thought of seeing my girlfriend again and find out she is with someone else. That would be equivalent to cheating considering that I was led to believe that she is waiting for me.

On the other hand, if you never led him to believe that you are together then he shouldn't have any claims over you and you have no obligations to inform him.

tell him and avoid him

Depends, is he dangerous? If so, talk to the cops about being afraid. (remember, I don't know what he did to get in there) If you think he is safe tell him now. If he thinks you're going to be together he is going to try to find you. Plus, if you loved him I think you owe it to him to tell him yourself. You had every right to find someone new, but he has a right to know (if you guy were keeping in contact that is)

I really think you should tell him as soon as possible because you are going to run into him!
although he's in jail, he's still a person and he deserves to know.

and you are in love with this new guy, love should be free and unbridled and I'm sure you'll feel much better after you tell him about it and clear up this whole situation and you'll be able to focus on your new love!

but remember if this guy really loves you he might not take it too well, have patience and tell him that this is what you really want, and hopefully he'll understand.

You should definitely tell him. Have you given him any reason to believe or assume that you will still be together when he leaves jail?

Is he a dangerous sort? Will he fly off the handle? All these questions you should ask before you work out the best way to tell him. I do think you should tell him though if you think he could handle it because it's better than running in to him one day (which you inevitably will, especially as you don't want to) and having to deal will the uncomfortable situation.

Be careful though and if you go to meet him to tell him then possibly take someone else will you though perhaps not your new boyfriend as that may rile him up.

my goodness I really think you should write him and tell him now. I have a friend in prison and his girl just dumped him by letter, but although it was hard on him, at least he's not got his hopes up for something that won't be there. Now he has had time to think and set other goals. Don't make him sit in there and think about goals and a life with you, if it's not gonna happen. If you tell him now, he can set other goals and maybe be over it by the time he gets out. Good Luck.