i have a very long-standing close friend who is a different type, but i see parts of his personality in me occasionaly and vice versa. he has some impact in decisions i make too, as i value his perspective very much and always consider his input. i was wondering if anyone else feels their friends/relationships have a significant effect on their personality and if this is somehow related to mbti?
MBTI is really just a description of various personality differences.
I think the longer you relate to someone (whether a romantic partner, family member, or friend), and the deeper your commitment is, the more you learn not just about how they work (which helps you tailor yourself to "mesh" better with them) but the more you yourself change.
When we are not tied to someone, if they rub us the wrong way, generally we leave. If you are committed to someone, when they rub you the wrong way, you'll try to stay and work it out. To work it out, you have to change... and often the "rubbing" will change your shape as well.
It sounds like your commitment to your friend leads you to view his differences positively... and you came to respect and even appreciate those differences, and incorporated the things you could into yourself. (Or you even learned how to channel the things YOU are in a different direction than normal, to mesh better with him.)
I think the largest growth patterns in my life came from refusing to leave relationships that involved someone different than me. I cared about them, so I tried to understand them and make it work; understanding them sometimes gave me conscious motivation to change; sometimes just trying to keep things alive changed things without me even being aware of it.
We do also become comfortable with people we know eventually. So the same things that originally might have bothered us or run us off eventually come to feel like "home" to us and we miss them when they're not around.