I'm jealous of hearing about engagements and hearing about married people
What about that makes you jealous?
I'm jealous that everyone seems to be engaged or married, but nobody shows me any attention.
When you're down, it's hard to see everyone else around you being happy.  The best solution, however, is not to be jealous but to instead work on changing the conditions in your own life that are making you unhappy!
You're right. Sometimes it's hard to know where to begin.
You could start by volunteering or joining a social group. You could also try counseling. Wallowing is not an option.