*Job Offer-What to do? Kinda Long!*

 So I've been working for the same company for going on 9 years now. I like my job, but sometimes debate whether or not I want to stay there *forever*. My work has been great to me, and I make decent $, but sometimes feel like there has to be more. Or it's not my *forever career.* I work Mon-Fri days now, but was thinking of picking up a couple of evenings a week in a different field, to try something different, without completely letting go of where I currently work. I know my boss wouldn't be overly ecstatic to hear I was working somewhere else, but at the same time, I know I wouldn't lose my job. So, with that being said, without even applying, a company in town heard I was looking, & offered me a job for a few evenings a week. It's in a similar field, but a step up from where I am now. The starting pay will likely be similar to what I currently make, but it would start at part-time, (on top of working my Mon-Fri day shifts at my current job). The only problem is, #1: It 'is' a similar field, and is that really what I want?? and #2: They require me to work Sundays. I put my availability for Mon-Sat. Evenings through-out the week, and whenever on Saturday. The reasoning behind having Sunday off, is to guarantee I get one day off per week, as well as it's the only guaranteed day off for my husband. So we like to spend it together. I told this to the employer of the new place, and she said I'd 'have' to be available Sundays to accept the position, & to think about it and get back to her this weekend. I'm really stuck, as to what the heck I should do! I think it would be interesting, & because it's similar, but different than my current position, I may find I like it more. The only major downside is working Sundays. Am I being totally ridiculous, turning a potentially 'better' job down, over having to work Sundays?? Any & all advice would help!!