Why do I feel like I'm imposing on everyone else's happy lives?

Because you yourself are not happy or they are simply making you feel that way.

Odds are you’re not very happy. Here’s the thing though. With the exception of your parents (in most cases), if you were imposing on people’s lives, you would no longer be invited to participate in their lives. People are not around you because they feel sorry for you, or out of pity or whatever. People are basically selfish creatures. If you were some how interfering with their happiness, you would be very directly and obviously cut out. Also, why on earth would you be imposing on someone’s happiness? Quite frankly it takes a lot of power to be the cause of one’s unhappiness, either that or it takes an incredible amount of purposeful meanness. We aren’t as important as we like to think. Stop worrying so much. People dont secretly dislike you or wish you were gone. People arent as subtle or as secretive as all that. Maybe you are. But most people arent.

Sound a bit depressed, and feeling a bit of self pity. I dnt mean that as an insult. I to feel the same way. I dont have a good answer, but if the feeling dosnt pass and you feel this way often, seek someone to open up and talk to.