The day will come when your child spends a night, or more, away from you. By the time they are almost three, you may well feel ready for it. Remember this isn't just about your feelings and needs, but your child's too. If they are able to be cared for by loving and reliable relatives like your parents, it's fun for them, and all a healthy part of growing up. One day you'll be dropping them off at school, and between now and then you need to graduate between 'they're with me all the time' to 'they're away from me every day, and going on a school trip, and playing at a friend's house'. It's better for them if they are cool about spending time away from you, and importantly that they know you're cool with it too.
Most people I know, including myself, had had an evening or weekend away from their child by the age of 2. That's not to say that you have to do it if you aren't comfortable. You don't have to do something just because others are doing it. But it is worth thinking about what it is that bothers you as he might be something that's rectifiable. Which would help you to be less anxious and let your child have a fun night with grandparents!
Your relationship is important. For you and your husband, and for your child. The fact that you can't see what the difference is between a night away as husband and wife, and a night away as a three, is quite telling. You could have a lovely romantic day with DH. A relaxed meal, wine, long deep conversations, afternoon sex, a long lay-in together. Loads of couple time. Which is good and healthy. I imagine your DH is a bit hurt that you have no wish to spend that time with him and would rather have DS with you like every other day.
If you aren't that keen on DH, then I can see why you wouldn't be bothered (and you then have other issues to think about) but I wonder if it's just that you've lost sight that you are a couple, and now only see him as the father of your child? SO many marriages suffer when that happens.
You have 9 months left so you don't have to rush to a decision. You may feel differently in a few months time.