I think self-pity in your case is very understandable and nothing to berate yourself for. But what Tommo suggested can be accomplished online. There is a lot of help that you can provide to others without leaving house. Not only online, but in person - you can probably tutor kids at your home, for pay or for free as volunteering.

Also, when the guy who chose the woman who agreed to live in his parents' house married that woman, you started hating yourself (per the OP). But why? It is not that he rejected YOU (even then it may not have been wise to hate yourself...), but he chose a more convenient arrangement. No reason to hate YOU because of that.