During my freshman year, I joined ZTA while my HS Sweetheart stayed independent. He just didn't get it. He could never understand why I had to be at the ZTA house every Sunday at 7pm for meetings instead of hanging out with him. He hated when I went on socials. Also, since we were together during my new member period, there were a lot of times that I had to be at the house for new member meetings, study hours, etc. He made it seem like I was choosing my sorority over him although it was my obligation to be at the house.
He refused to go to my semi-formal since there would "a lot of annoying frat boys there".
His roommate, who I have still remained friends with (well...he is engaged to my best friend), told him, "You need to be more supportive of ZTAngel's involvement. You need to go with her to formals and date functions and stop giving her a hard time when she goes to socials. If you don't, she's just going to get more aggravated and she'll end up meeting some fraternity guy who is 100% supportive, she'll end up cheating on you with him, and that will be it."
Of course, my boyfriend took what his roommate said with a grain of salt. The weirdest thing is that his roommate was totally correct in his assumption of what would end up happening. I eventually got really tired of my boyfriend getting on my case about my sorority involvement. I went to a social, met a guy in a fraternity who 'wooed me' (and who of course I understood why my sorority was important to me). And, oops, ended up cheating my boyfriend.

Needless to say, me and the boyfriend broke up. Best decision I ever made. After that, the guys I dated were all in fraternities. I liked it more because I never had to justify my sorority involvement to them...they already understood.
For 2 1/2 years, I have been dating a Kappa Sig. He never gets on my case when I have to sorority stuff.