I know I should probably hate you, but I don't. You've done nothing wrong. Right now, you're probably deliriously happy, holding onto his arm as he takes you out to dinner. The two of you may be in love. Maybe he makes your heart flutter, and he thinks that one day he'll ask you that special question. Ha! He just hasn't met me yet. Even though I don't know his name, and I've never actually seen him, I know my future husband's out there right now. Despite the fact that you currently claim him as your boyfriend, it won't be long before I make my move. In fact, by the time I come along, you'll probably be long gone. The breakup was probably over some trivial thing, that you both cared about just enough to realize that it wasn't working.
However, right now, he's yours. He's holding onto your hand and looking into your eyes. In that case, I have a couple of favors to ask. Please take care of him. Don't worry about breaking his heart, I can fix that, but remember that you're an important part of his path to me. Right now, he needs your support. Remind him that he can do whatever he sets his mind to. Let him know that you like him just as much as you love him. Please steer him away from drugs. Don't let him make any lifelong decisions he'll later come to regret. When I meet the love of my life, I'd appreciate it if he's in one piece.
As for you, don't be discouraged. You may be harboring a grudge against me for stealing your man, but I wouldn't take it too hard. Because, at this very moment, you're future husband's out there too. He may also be in a relationship, but I wouldn't worry about that either. It's not going to work out between them, because sooner or later, he's going to meet you. And the rest, as they say, is history.