Breakups can be really damaging, and sometimes we end up taking a while to get our lives back in order. When that happens, sometimes we're faced with the horrible question: what if it's too late? Have I lost my chance with him? Oh no, what if I missed my chance? Here, I'll answer those questions for you.
First of all, let me reassure you that very rarely is a relationship impossible to recover. I've seen all kinds of people have all kinds of problems and still get back together. Some situations do admittedly end up showing themselves to be un-salvageable, but the odds are greatly in your favor that there's nothing stopping you from getting him back aside from your efforts and his resistance to it. This doesn't mean it's necessarily going to be easy...but the most likely fact is that your situation is redeemable.
However, that said...sometimes there is a little bit of a time limit on these things. It's more circumstantial than it is a set "expiration date" or "statute of limitations." I've known people who've emailed me and told me that they've actually gotten back together with their exes of fourteen years ago...that's definitely outside my particular realm of expertise, but it just goes to show that many things are possible and simple time may not necessarily mean all chances are lost.
The sort of situations I'm talking about though, in which it may be better to leave things be and try to move on with your life, are when it's very clear that your ex has moved on with his. Breaking up marriages or ruining healthy and serious new relationships...it gets to a point where it's just selfish to pursue your ex and if you really love him you may have to come to terms with the possibility that you two weren't meant to be together.
However, those cases are rare and as I said earlier, the odds are in your favor that barring extreme circumstances like that you have a full chance at winning him back and ending up very happy with him.