I have been married for 25 years and hobbying for the last 5 years. For me, it is a result of being bored in my sexual life. My SO and I have sex regularly at least once a week, but it is kind of a "duty" now than spontaneous love making. There are certain things my SO will no longer do, such as BJ or allow DATY, so this is what I seek in the hobby.
I will agree with other posts that once we had children the frequency declined and had to be planned to fit into our schedules. Now that the kids are grown and out of the house, the frequency did not pick up. This doesn't mean I don't love my SO, we are just at a different point in our relationship, which I find very comfortable. She still is my best friend and we share significant history.
With that said, I don't let my hobby life enter my personal life. The hobby is just that for me, a hobby. I seek out some fun times and experiences that I would not normally have. My SO does the same, she has her own hobbies (not THE hobby) and interests where I have no involvement. I think it is important to grow as individuals, while maintaining a loving relationship, and to me that is the bottom line.
If you set your priorities on what is important to you and don't confuse or intertwine your SO relationship to your hobby relationship, you can make both work.
I have been happier these last 5 years and it directly reflects on a better relationship with my SO. All she knows is that I am happier and easier to live with and that is her bottom line.
Good luck on your marriage, I wish you the best.