Do you find him hurting your feelings alot? With bluntness/directness and all?
No, not actually. He is very gentle with me. And most of time he is joking or sarcastic so most of time I don't take him too seriously. I think he appreciates me being very different and tries to understand me.
I give him space because I require space too. I'll give him freedom to do most things he want to do. I have no desire in controlling him. I trust him. He can be very blunt but apparantly he appreciates and/or understands me better not to be too blunt. And sometimes if he is, I don't really take it so seriously. The thing is just working with us two for some reason, cannot really put my finger on it.
From the two ISTPs I know here... the common observation was they would not actively seek out the relationship themselves, ergo, you'd need a partner who'd act to bring them into one, yet in a way which does not make the ISTP feel like he's losing control - rather, a more gentle yet firm guiding that helps them realise they are better off with that person, so they'd stay in it from a cost-benefit analysis.
But to evoke real feelings from an ISTP, I think you have to bypass that cost-benefit mindset, and difficult as it is, to engage their emotions. That is the spark they miss, and I feel, that is the spark that makes them stay with one person more than any cost/benefit can: someone who understands and is able to draw out their emotions, in a way, bringing colour to them.
In that respect, I think an I/mild E would work well, a J softened by Fe - to set the boundaries and yet have patience without losing direction. The ISTP cannot feel manipulated as his trust is easy to lose.
I would go for an N though, vs. an S - the intuitive is better able to show possibilities I feel, and would create more growth for an ISTP - I feel with a fellow S, they could easily fall into a trap of routine and fail to express fully and thus take the other for granted.
I could see Ti being a nice match, if paired with N, as the thought processes would feel similar, yet from a new angle which could be intriguing.