If you're not attending to your personal fitness then the situation you're in is dysfunctional, regardless of whether or not it's a family, a childless relationship, or single life. So it's not possible to sacrifice personal fitness for family function because that is a core part of it.

If you're taking care of others to the exclusion of yourself, you're going to end up in a downward spiral of resentment. Nothing good will come of that.