I was with an SEI for 7 years. It was easy, comfortable and conflict-free. I ended it because I got bored, felt stagnant and craved for something deeper that I couldn't put into words. Only years later after getting into socionics I realized this unnamed craving was Ni dual-seeking. I think from her point of view I was close enough to an ILE (especially due to my C subtype and alpha parents), and the Se leading didn't really bother her as it coincides with many traditionally masculine traits. Her subtype was most likely Normalizing.

It's an easy "trap" to fall into, because SEI very good at pleasing your physical desires, will not judge you and the creative Ti/Fe HA <-> creative Fe/Ti HA interaction is very enjoyable for both partners.
I did regret breaking up with her sometimes afterwards and most of all I deeply regretted hurting her in the process, but I think in my case it was sadly inevitable. It's a good compatibility nonetheless, you could do much worse and it all depends on how deep your craving for Ni is and if you could satisfy it some other way.

The biggest problem is that Se and Si leading have completely opposite feelings about what constitutes a good life, so despite very good interactions there is a fundamental difference in what you desire in life.