Mike, I've walked with my husband and without. Both good and very different.
If you go with someone you assume some responsibility for that person and they for you. Do you want that? It also means that decisions must be negotiated - or at least they should be, and even that can become contentious. There is someone to share the good outcomes, which can be great, but also someone to blame for all the ills that are par for the course. When you are by yourself you make the decisions, no consultation, and you are responsible for the consequences. It is common sense really but takes on intensity on the Camino, with the physical and mental testing it involves.
The good side of having a companion is the wonderful shared experiences and the deeper understanding of each other.
There are other considerations that I think are of lesser importance in making the decision, but may be useful to think about. Your walking speed and endurance will vary (not a big issue IMO - you can always meet up at the next bar). You may want solitude and meditation time (again not a big issue - it tends to happen anyway, see previous point). Generally a shared private room will cost very little more than 2 places in a private albergue. Pack weight can be less as you can share the soap, toothpaste, sunburn cream. One person can do the washing while the other cooks a meal. If something goes wrong, injury or illness, help is on tap.
I'm inclined to agree you should go with your gut instinct but it's tricky if that threatens the relationship. Compromises are possible; I nearly always used to walk part of my Caminos with my husband, and part alone, as he could not take as much time away from work. It worked well for us.