I also wanted to add one more thing that might be helpful. It's another analogy similar to Finasel's which I felt was really good encouragement.

When I was learning to play piano, I had no problems learning the right hand portion of a measure, and no issues learning the left hand. The problem was trying to put both together, which was a learning process all on its own. It's kind of the same with healing and DPSing. We can look at learning the right hand as 'healing', and learning the left hand as 'DPS'. After becoming proficient at both, it is time to put both together to bring out the song's true potential. One hand sounds nice, and is pleasant. Same with the other. But together? Amazing!

And that's what healer/DPS is. It is truly a harmony of performing 100% in each role which makes you ridiculously powerful.