So, should I confront him, contact my teacher, or just accept the situation?
Let me first summarize my view of the situation. You and your partner were both given a total amount X of work to split among you. And he, instead of doing X/2 and leaving the other X/2 for you to do, did the whole of X himself.
Is that a bad thing? Well, yes and no. Although it certainly suggests some negligence and selfishness on the part of your partner in that he did your part of the project without any consultation or consideration for you, it is also impressive in a way. He did twice the amount of work he was expected to! So while I do not mean to suggest that your feelings (sadness, anger etc) are invalid, some of the other answers suggesting that your partner is a bad partner and someone unworthy of fraternizing or collaborating with seem misguided to me. In fact, I think your partner has the potential to be a rather awesome partner and collaborator in the future, once he is made aware of his immature behavior in connection with the current project and reflects on it a bit. Honestly, I don’t think that will be a hard lesson for him to learn, assuming he is not an inherently selfish person.
About the current project, I think there is a likely solution that will be a win-win for everyone: you, the partner, and the instructor. You and the partner should talk to the instructor, explain what happened, and ask for suggestions for broadening the scope of the project to roughly 3X/2. This additional scope could then be your part of the assignment, which hopefully will have as much value for you in terms of the learning you can derive from it as the original assignment. Ideally, during this conversation your partner should apologize for his lack of consideration and for putting both you and the instructor in an awkward position. I’m reasonably confident the instructor will be happy to accept such an apology and not penalize either of you for this situation.
Of course, to make this happen you will have to talk to your partner. I wouldn’t describe this as “confronting” your partner as that sounds rather adversarial. You should simply explain to him how his behavior has deprived you of a valuable learning opportunity and the satisfaction of doing an interesting assignment, and suggest how to move on from there.
If this arrangement works out, everybody will benefit, and I think you and your partner stand to get an excellent grade for doing a project that is well beyond the scope of the original assignment. I can’t guarantee the instructor will cooperate, but it’s not clear to me what else they could do that isn’t clearly penalizing you for something that’s not your fault. Anyway, good luck, and I hope things turn out well!