Well, you’ve been able to articulate your problem to me really well — I think you should just come out and tell your boyfriend exactly what you’ve told me, that you miss the way the two of you used to be, and for the last year and a half, it seems like he’s not happy with you, and that’s made you feel really rotten. Don’t blame him when you say any of this, and don’t pass judgment. Your tone should be sad not angry, and your intention should be to communicate, learn his feelings and see if there’s a problem between you to solve.
Then, (and here’s the trick) ask him what he thinks about what you’ve just said. It’s very important that he feels heard, and that you listen to him.
Either you’ll be bringing your feelings and this problem to him for the first time (stranger things have happened!) or he’ll be able to enlighten you on what’s going on with him, which is crucial to problem solving.
If after this conversation (or series of conversations), you feel like there’s still a relationship to be had between the two of you, figure out together, what needs to change, and if you’re both willing to make the changes required for a better time together. If not, your relationship may have run it’s course, and you’re no longer compatible, but you’ll never know unless you communicate clearly with him.
I hope this helps. I wish you good luck, and hope you’ll let me know how things go.