Although the ISTP does not usually have a well-developed Feeling side, they frequently do have intense feelings for people. They can feel overpowering love for their mates, although they are likely not to express their emotions, or to express them inadequately or inappropriately if they do venture towards expression. However, unlike many of the other personality types, ISTPs feel strong affections one day at a time. One day, they may feel completely, intensely in love with their mate, and the next day they may be totally disinterested, or perhaps even ready to move on. This "live for the moment" type of approach is different from how most other types experience their feelings, and is difficult for many to understand. Consequently, the ISTP may be called "fickle" or "cold". In fact, they are not really fickle, and certainly not cold. They simply experience their lives on a moment by moment basis, and go along with it's natural flow. However, since most people need more commitment than can be offered when taking things day-by-day, the ISTP who wants to remain in a relationship will have to resolve themself towards being involved in a more traditional commitment. For most ISTPs, making a commitment to an intimate relationship will require an effort to stretch themselves outside of their comfort zones. However, those who do so will realize that they can enjoy the benefits of a strong, committed relationship and still live their lives in the present tense.

So that's the love life of an ISTP personality type. And yes, I am an ISTP. To put it short, ISTPs are tsunderes.  I'm so sorry for my future partners/lovers if I'm such a pain in the ass.