Do you lose muscle if you don't exercise for just 2–3 weeks?

‌I am in my early 50s
and living with a diabetes diagnosis.
I take medication every day and exercise as well.
About 2–3 weeks ago, an acquaintance returned from abroad, so there were many occasions to drink,
and I let my guard down.
I used to walk over 8,000 steps every day, do about 100 squats, and 30 minutes of moderate-intensity indoor cycling.
After doing this for a few months, my thighs became firm and it felt great,
but after resting for a few weeks, it feels like my thighs aren't as strong as they used to be even when I flex them.
Yesterday was a drinking day too.
I want to exercise hard and control my diet,
and my doctor told me to just keep eating as I am and focus on exercising hard,
but now that I've let my guard down, it's not easy to start again.