I actually had a talk along these lines with my wife a few days ago after having to spend about 30 minutes getting from the usual "what's wrong" "nothing" to getting the truth out that she felt I put my friends (who I go jamming with) before her and our son.
The thing is that I work on average 18 hour days being a mad IT geek, and pretty much all my effort is going into a big project that if it works out, will mean we (as a family) are pretty much set for the next 20 years. She doesn't really notice this since I work from home, so I'm around and I do some bits around the house, entertain my son (at the moment mostly just making funny faces at him since he gets a kick out of it), and so on and so forth, but when she and son go sleep, I'm still working.
She basically didn't know - she thought I was just spending all night playing bass and goofing off, since usually in the morning before I sleep is when I put in some practice, so she often wakes up to see me sitting in my office jamming it up a little.
So that got talked out, and then the next thing came up: "it's not fair that you can go do stuff and i can't"; and that's what was at the root of the whole situation in the first place. A 5 month old son that's being breastfed pretty much means that if she wants to go do something, he's going to have to come along for the ride; unfortunately my wife suffers from not having a hobby of her own, which is sort of fueling that "you can and i can't" fire. That's being worked on, though.
I did tell her that I didn't know she felt that way, so I asked her if instead of me going out to meet my friends to jam if it was okay if they came to the house instead; funny fact: we're both sitting there going "oh, huh, that's actually a really good idea". Nobody thought of it before. In the end we agreed that sure I could go, but if I do go, take her along and drop her off at her brothers house so she can hang out with friends there, and take her for dinner after I'm done jamming/practicing.
Long story short: find a compromise that you can both live with; after all, marriage is all about compromising to both enjoy your life together.