I don’t think I could ever do this.
Then you're the world's biggest puss. There's no pain outside of getting the shot and the shot literally feels the same way anywhere on your body. The one I got on my balls felt like the ones I got in my mouth, which felt like the one I got in my knee, which felt like the one I got in my ankle. It's a quick pinch sensation followed by a little bit of pressure while the meds start to work. It was 30 minutes of what I would call mild displeasure, but it's not like being hit in the balls pain, it's I'm having a medical procedure pain. Getting a dental filling is worse, getting a crown and root canal are significantly worse and they are tolerable.
If you don't think you can do it, ask your lady about her side effects from an implant, if she has one. Or read about uterine cysts which can be caused by nearly any form of medicated birth control she may use. Ask her to tell you how BCP makes her feel. If you're really up for being shocked, read about tubal ligation.
Trust me, we have it easy and get to be heroes for doing it.