You spend a lot of time together.

For example, you work together - get up at the same time, get to work in the same transport, and are in each other's field of vision all day. It is not surprising that when you come home, you want to be alone for a little while. If you are with each other almost around the clock, then fatigue and irritation are quite expected feelings. You just don't have time to miss each other. There can be only one solution: try to see each other less often. For example, if you work at home, sit in different rooms. If you get into the habit of getting to work together, use different modes of transport or arrange for one of you to come to work a little earlier. Basically, improvise.