Don't give up. INTPs are some really great people. Look at them like this: INFPs and INTPs have the same engine, but said engine runs off of a different fuel for each.
How do they show affection? Well from what I've seen they are private about the whole... Feely thing. One thing I think is INTP affection is when they carry on an intellegent conversation with you. This is saying to you that you are worthy to them in their mind, that you are intellegent. Another way to see that they care is if they let you in on their personal lives, what they are passionate about. But that goes with anyone.
You are doing good if you change their logic. This shows them even more that you are intellegent, and in term will earn you more respect.
An obstacle you will have to get over is the fact that if you are going through a hard time, they will still use their T. The worst thing is to get offended by this. A good example of an INTP trying to comfort me:
me: "Man... I can't believe that I crashed my car. This really sucks, I feel like shit."
Him: "Well, you could sell the car's parts that are in good condition to make some money to help pay for the ticket, and eventually a new car. You also are going to be getting taken to school by your parents, so you won't have to spend money on gas, seeing as how gas is outrageous right now."
me: "Yeah... That's true. I could do that. I feel so stupid though, I was only going like 25."
him: "Blah. Well it was just bad luck, you have your head in the clouds a lot, and that gas station is crowded a lot of the time."
me: "Yeah I guess..."
him: "Look on the bright side, at least you only dented their van. You don't have to pay for that."
etc...
They really are trying to help you, just in their own way. Watch out for this, and accept that they are trying to be helpful and that they care.
I hope I helped. I'm an INFP if you didn't notice.