I am an introvert myself but I am also in a marriage where I tend to socialize on my own pretty frequently. Actually it's only been in the last couple years that I realized the prevalence of the expectation that couples generally go to social things as a unit, even outside of weddings. Anyway, I don't think your setup has to feel awkward nor that you have to cut back on your own outings.
You can stop making excuses for your husband, but there is a middle ground between polite white lies and too much specificity about exactly why he's not there. If people ask where he is, try to take it as though they're politely inquiring that they hope he's well and not that they're insulted that he declined their invitation. You can pull out responses like these:
- "Oh, he ended up having other plans." (this might sound weird to extroverts but spending quiet time by yourself is a legit plan to introverts)
- "He wasn't feeling up for it this time, but wanted me to come anyway."
- "Large parties aren't really his thing, but I'm the opposite and get really energized by getting to hang out with so many people."
Just because people are asking about him not being there doesn't mean that you have to change your marital agreement that "He doesn’t mind if I socialize and I do not care if he takes a pass on 99% of the invitations sent our way." Just be cheerful and matter-of-fact about it. If you're fine with it, it shouldn't matter if other people think it's unusual. I have a brother-in-law who we all know doesn't especially enjoy long extended family events and we all just jokingly describe him as "an indoor cat."
Also, yes, it's not your responsibility to reassure others about whether your husband enjoys their company or not. You can suggest that you all get together for smaller social outings, but really, you only have to convey that you are excited to be there with them. I think the Captain Awkward advice of asking him to stop by for a few minutes to a neighborhood thing every so often is perfectly reasonable, but you don't have to take on the emotional labor for everyone involved.
