I've been a SAHM, WAHM (with a home biz), work part-time and work full time (as a single mom then) ... I must say there are challenges to each.
In order to help your relationship, i suggest you write down everything you do ... EVERYTHING as a SAHM. Approach it like any out-of-the-home job and make a job description and schedule for every day of your week and what household chores you accomplish on those days. Include everything from laundry to picking up dry cleaning and the time estimates for these jobs (it's okay to overestimate a little bit to allow for changes in the schedule). Also include scheduled play times with your daughter, meal preparation, picking up dry cleaning, and more. As with any job, try to do as much as you can in the time allotted (as I'm sure you do!).
If you're a SAHM, there should, hopefully, be very little you are asking your husband to do on his chore list. When I was a SAHM, I even mowed the lawn & washed cars, but not everyone does that. LOL ... Trust me, that went a LONG way toward showing my value to him ... ALSO, make sure you add on that list/schedule the things your husband does, including his job and the chores he currently he does or you ask him to take care of and block the times off that is needed for him to do those things on the schedule as well. Fair is fair.
Something has to be done whether it's a change in your and/or his approach to your job (being a SAHM) or a shifting of responsibilities ... He may be resentful of all the time you are with the kids while he feels you are "just" staying home. I feel you!!!! I know that being a SAHM was a VERY difficult job many days. There was no break, little emotional support, and no adults to talk to. LOL ... "water cooler" conversations can be therapeutic at times.
SO, after making the current schedule of all the family job responsibilities (yours and hubby's) including the jobs you do as a SAHM, you'll make the same schedules showing how life would change if your family adopted a different choice. Men are generally very pragmatic so maybe make a list of pros & cons for each of these showing facts and numbers, not feelings and fears (Use: financial benefit, preserved family time on weekends/evenings, lower tax brackets, etc. Do not use: missing baby, other people watching, kids getting sick, etc.). ya' know?
The options would be:
1. SAHM/Status quo: This means the schedule you just created stays the same. This is NOT the ostrich approach (put head in sand and forget) because that's rarely useful. It's a truthful evaluation of the work you do as a SAHM. Try to take as much home responsibility from your husband so he can enjoy the benefit of having a wife at home!! Maybe there's something else you can do for him to make him feel taken care of ... Sounds cliche to have a newspaper and dinner waiting like June Cleaver, but you'd be surprised how happy simple things like that can be. If comes home to more work after a 'long day at the office', this may be what causes the resentment.
2. Work part-time: In this case, you'll have to fit the work you currently do into the evenings and weekends. You would still have much of the responsibilities, but some of the work should then be shifted to your husband.
3. Work full-time: divide up all of the household chores and errands and put them on the calendar. He may start to see your value here. As a working single mom now, this is what MY schedule has looked like for 10 years and it's nuts. LOL ...
Maybe after having a calm discussion about this and after reviewing these scenarios your hubby might be more understanding or accepting of you being a SAHM. BUT, if he does NOT, then by all means consider going back to work. His feelings are just as valuable as yours and if he is resenting you staying home, then it's time for a re-evaluation of this situation. You didn't say how long you stayed home when you had your son. if you were home for a year and a half and then went back to work, he may be wondering why you are reluctant to do the same with your second kid.
Sorry this is so long-winded, but I hope that you are able to resolve this issue in an amicable and loving way so your relationship with your hubby can grow!!!