Before you enter stepparent role, don't underestimate the impact of custody schedule on your life...
I personally have a 50/50 custody arrangement, with the switch occurring on Fridays, and during long vacations, it's 2 weeks on/2 weeks off. I had no idea how difficult it could be before I entered this role.
At first, 50/50 custody seems like a good compromise. For one week, you have your partner to yourself, and for the other week, you deal with the stepchild (SK) somehow. However, in reality, it has impacted my life more than I expected.
I have to plan everything carefully according to the schedule. There is no room for spontaneity or for planning something with my partner whenever an interesting event arises because there may be a child with us. This means I either have to go alone or not go at all.
My partner has to take vacation days for the stepchild, and those days are not for us. So, we really have limited time to enjoy vacation days just the two of us. Some days, I end up spending alone.
Have you found an amazing travel deal? Wonderful! However, if the trip is from Wednesday to Wednesday, you can either go alone or not go at all because it's difficult to arrange for the child during that time.
Is it the HCBM’s week, but she can't pick up the child from school? Then it's your partner who has to handle that.
Is there a family event or holiday, but HCBM forbids you from taking SK to your family? Go alone or stay at home.
Is your partner exhausted or needs some time alone? You can be sure that he will want to do that during his week off.
Do you dream about a long, 2-3 week vacation together? Cool! Take whoever you want, but not your partner.
Looking at it from this perspective, the reality of stepparenting is significantly harder than I expected, even though I was really considerate. All I can say is, if you have doubts, it's definitely not for you. Before entering the role, you have to be more than sure that you are okay with sacrifices on each possible field.