Your needs for time may vary
One person needs to make frequent appointments to feel closeness, and the other person needs to have time alone to relax and enjoy the next meeting. Spending less time together doesn't mean your relationship is less important, and saying you want to be alone doesn't automatically mean you're rejecting your partner.
Of course, situations in which promises are repeatedly canceled or one party's needs continue to be ignored need to be looked at separately. Don't assume meaning based on a single request, but talk about what patterns follow and what the implications are.
Explain the time needed
Instead of saying something that might sound like “I want to stop seeing you,” try to be specific about how alone time helps you. You can include your current needs and your next plans together in one sentence, such as “I want to rest quietly today. I want to have dinner together tomorrow.”
The person who wants to be together can also convey their request without turning it into an accusation. Suggesting something like, “It makes me feel better to know your weekend plans in advance. Can we decide on a time we would like to spend together this week?” leaves space for the other person to choose and respond.
Create a rhythm to keep together
Make repeatable appointments that take into account each other's schedules and energies. For example, you could briefly say hello during the week and spend a day together on the weekend, but rearrange your relationship in advance during busy weeks. The important thing is not to force equal amounts of time, but to find a standard that you both feel is predictable and comfortable with.
Check to see if one side is giving in every time. If the rhythm you've established feels burdensome or lonely, you can take it as a sign to readjust rather than seeing it as a failure. Try updating your agreement by asking, “How have things been going this way over the last few weeks?”
MBTI's extroversion/introversion preferences do not fully explain a person's social needs. Rather than deciding that some people always want people and others should be alone based on their type, it is more accurate to check the person's actual experience.