Commitment is not a strong point for the ESTP. Living almost entirely in the present moment, they're not comfortable with making plans far in advance for their future. If this tendency is not addressed in the ESTP, they may fall into a pattern of jumping from relationship to relationship without ever making a real commitment. If this is okay with the ESTP, then that behavior is fine. Most people at some point in their lives do wish to settle down. If the ESTP reaches that point, there's no reason they can't make a commitment as long as they consciously renew it to themselves daily.
They take things on a day-by-day basis, and are uncomfortable thinking too much about the future, or making plans far in advance. For this reason, ESFPs are not natural long-term commitment people. They may feel tremendously committed on a day-by-day basis, but they do not naturally plan for their futures. This commitment issue is a potential pitfall for the ESFP. Many people of this type overcome this potential weakness, and become involved in truly satisfying, lifelong relationships. Others do not address this weakness, and move from relationship to relationship without forming real commitments, convincing themselves that this is what they truly want.
ISTPs take their commitments on a day-by-day basis. Even if they say "I do", it usually means "I do for now". They do not like to make lifelong commitments, although they may very well be involved in lifelong relationships which they have taken one day at a time.
ISFPs are warm and giving people, who have a depth of emotion and caring which is not often obvious to others, except those who know them extremely well. They are usually intense people, who experience their emotions on an intense level. Although they may appear to be light-hearted, they are in fact extremely serious, and take their relationships seriously. Unlike other SP types, people with the ISFP type desire and seek lifelong, committed relationships.