I know how you feel! I'm not possesive, but more the jealous type. I guess it's partly because I was in love with someone else whilst with my ex (didn't act on it until me and my ex were well and truly over, after him being a complete a**hole!) I avoided the guy I liked (who also happened to be my best mate - HOW complicated?!) and it just scared me that although I was completely smitten with and devoted to my ex (who I was with for 14 months) and yet I somehow managed to fall in love with my best mate (although he's such a lovely bloke that everyone was telling me to just dump my ex and be with him. I couldn't do that, though because I still loved my ex). Basically, it's not my boyfriend I don't trust; it's human nature and the way we can fall in love so easily, even when committed to the 'love of my life'.