You will receive that one thing that you aren’t thinking about, their time. They may give up certain activities to spend time with you. Being alone is an activity, and if they give that up (not totally, they are still kind of human) to be with you it could be love or they have strong feelings toward you that can possibly be misconstrued as love but the potential is definitely there.
INTJ’s want efficiency and optimisation so if you find them doing things to help your life run more smoothly or them getting you items to the same the effect then it’s a safe bet that they care deeply for you, love is still up for debate but that’s probably where its going to end up.
TL:DR. They’ll spend time with you, they’ll get you stuff (more functional than romantic)