I agree on the card issue. You don't need to make any excuses, and it's okay to be angry with yourself. Now is a good time to move forward and act anyway.
Your son's admission makes me wonder how much that might have been playing into his depression lately. I am glad he felt comfortable enough with you to share that with you, says a lot about what an awesome mom you are! I think it's perfectly reasonable to worry for him, when the world is not always so accepting of folks who are "out of the ordinary". If he's willing to talk more, just asking him questions about how he's feeling, if there's somebody he likes etc. will probably mean a lot to him. You do not seem to me like someone who would make him feel accused of some wrong-doing.