It seems as though 11 years have gone by without either of you figuring out what the other person needs. Communication can be extremely hard for an ENTP/ISTP couple, as the former seeks confrontation immediately and the latter needs an endless amount of introspection before even getting to the point of verbalizing the issue. Both types put a great deal of importance on mutual respect, so it must be a relationship actively focused on the give-and-take balance.
While ENTPs can easily compartmentalize and move on from the past, ISTPs tend to overvalue their investment and it creatives internal conflict. "If I spent so much time and energy on this relationship, but it ends up being a failure, how can I trust myself to make good decisions in the future? How can I justify those lost years?" says the ISTP, but never out loud. ENTPs can be great motivators in getting the perpetually indecisive ISTPs to reach a concrete conclusion. Unless you both put in a LOT of hard work to repair 11 years of frustration, you might have to be the "bad guy" and save both of you from more turmoil by cutting the cord. While you may have the luxury of flexibility and selective memory, ISTPs n.e.v.e.r forget and are prone to never letting go of their first impressions or perceptions, no matter how much compelling, conflicting evidence they are presented with. I think the ship has sailed on your opportunity to establish a necessary foundation...
Side note: I'm not intentionally trying to make ISTPs sound terrible, it just happens that their weaknesses apply to this situation. ISTPs can be fiercely loyal, thoughtful partners that often ignore their own issues to give their partner unwavering support in trying times. When they truly like the person they love, they are highly capable of long-term commitment. That's not to say they make it easy, but they certainly put forth a conscious effort to make their hard shell worth cracking.
