Interesting questions. I'll briefly sketch out my situation then reply:
I'm 60 and divorced. Have assets from my divorce (IRA, will get a third of my ex's pension, have $300 k equity in my $500 k home). Still getting some of my kids through college and have my own business. Receive alimony which will stop in 2 years.
BF of 3+ years - a wonderful man who sadly lost a big chunk of his adulthood to addiction. He's 6 years sober now and doing great. However he started with NOTHING when I met him. I made it clear that while I had enough to fund MY retirement, I couldn't carry him too and he needed to get his financial act together to be able to contribute (he's 7 years younger btw.) He doesn't live with me, but he has also started his own business, supports himself, and in the last 3 1/2 years has acquired all the NICE furnishings for his very nice rented apartment nearby, a huge TV (and a almost-as-huge one that he handed down to me lol), a used BMW wagon which he has fixed up, tons of clothes, fishing rods and reels, other toys, and $5,000 in savings.
A. If or how your FIRE numbers changed once your SO got on board?
I expect his retirement to only be able to fund his basic living expenses, so I have to think of the house etc as all on me. However, it would also have been on me if I was single.
B. Similarly, once you went from single to 'not-single', did your FIRE number and/or timeline change?
I'm a little late to be retiring early, but the truth is, I COULD retire today if I did not have so many people depending on me (adult kids in college, elderly mom living with me, etc.) BF doesn't affect that equation much, except that in the future, it might lead me to one more year syndrome if his savings isn't looking good enough
C. Did your rate of savings increase, decrease, or stay the same?
Since we do not currently share living expenses, he doesn't affect my savings rate by that much. I saved a little less the first year we were together as I helped him to get on his feet, but I save more now because he helps me with household maintenance chores. I have also ramped up my savings more in anticipation of the fact that I am solely responsible for my retirement and might have to help him too
D. What were some of the biggest setbacks and advantages?
He knew nothing about being a financially responsible adult and I have had to teach him. He still shops way too much and buys too much stuff but he has improved dramatically over the years. He is not in debt and he is starting to save and get out of his scarcity mindset. Advantages are having a loving partner who totally has my back if I need help with anything, like taking my mom to the doctor etc.
E. Did you keep things separate (and private), or combine and share everything?
Since we don't live together we keep things separate. I know all about HIS finances but he doesn't know all the details about mine - I'm reluctant to share actual figures with him because I don't want him to think "Oh, she has plenty of money, she can help me" when actually it's just enough for a reasonably comfortable retirement for one. Don't get me wrong - I would help him if needed, but what he really needs right now is the lessons of financial independence and self-sufficiency.
F. Any major disagreements such as wanting to buy vs. rent, invest in the stock market vs. real estate?
Most disagreements have been about his spendy ways. Since he's spending his own money I really have limited room to complain, but I try to help him see that the goal is for him to be able to save enough to retire with me someday. I lead by example. He's actually improved dramatically in this regard, he's just having to learn lessons about responsible adult finances that most of us learned in our 20's. I expect in the future, when we finally DO live together, there will be more potential for discord as we are both strong-willed people. I anticipate keeping our finances separate even then to minimize the stress. I will probably pay all the housing costs and utilities that I do now anyway, but expect him to continue to pay for his own car, insurance, clothes, medical etc. Since he is younger he can work for several more years to build up assets, and without having to pay for housing, his social security will cover a lot of his expenses in the future.