I'm never been in a relationship with an INTP but I have two IxTP siblings. I don't really have a Susy Sunshine reply, but here it is.
The obliviousness can be so strong that you wonder if they're doing it on purpose. Since they're my bro and sis, the relationship is familial and not romantic so I've learned not to take it personally, but I don't believe you should be required to do such a thing in a romantic relationship.
You've gotten advice to just tell you SO person, but I understand as another Fe-dom that you wish they would just notice without prompting, without you having to explicitly tell them, break it down for them, explain to them why something is necessary or why you want them to do something. You feel like you've got to write a critical exegesis to do simple shit and that can be exhausting and sometimes I think done just to tire you out and get you off their backs.
When they don't notice, it's very easy to believe they don't care. And to be honest, sometimes they don't care; it's not viewed as important and it they will become stubborn mules and absolutely intractable if they feel like you're forcing them to do something. I have often felt like I'm always nagging at them to do what I view as simple relational things, that I've just given up and learned to do without. Like I said, I've decided that's not something I'm going to deal with romantically. That's your choice to make because high chances are it will continue unless you can make them see how and why it's important.
I'm going to say a little story that really was a revelation to me. I was a senior in high school and had gotten my first C in a class. I had never gotten anything lower than a B before and I had been coming home complaining of how hard that class was for me and how I just wasn't getting it. My sis was 17 and my bro was 15 and we all got our report cards in the mail. As soon as I saw that C, I burst into tears and they looked at me and started laughing. Of course, I started Fe-raging at them and they saw that I meant business but I guess over the years I came to see that moment as insight into what their instinctual responses are. They've smoothed out considerably over the years, but their baseline response to most things is just not to see the emotional value in situations. But don't want to necessarily pin that on ITPs, because many people are like that.
If you're looking for more attentiveness it's going to have to be an internal revelation they reach on their own. Or, and once again I'm going to be honest, you've got to be very subtle in how you "get" them to do better. My INFJ friend's boyfriend is ISTP and she's had to sit and ponder strategies to make him more attentive towards her...how to switch a light on inside of him to pay attention to their relationship. That's more work than I want to do, but if you're willing to do that then do so. There are both positives and negatives to going with the flow and while I agree most IxTPs in my experience and low maintenance, unfussy people their particular strain of passivity can be difficult to surmount.