Hello Jenny,
It's normal to be scared, it's normal at any age but I can totally relate to your situation. I've had Crohn for 13 years now, and a stoma since my first flare. I've never really had the time to ponder over the idea of having or not a stome. In my case it was pretty much a have it done or die slowly as I was literally losing all my blood and the treatment really were not working and making me sicker if anything.
I have to say I was scared of how others would see me. I was 14 so you can probably imagine how scary it was for me to start dating after that? I mean, I've never really known the dating before so for me it has always been the dating after. I never really felt sorry for myself because I had a bag. Despite that though, from 19 an up, I've rarely been single and when I was, it was by choice. It is something you will have to be discussing with your boyfriend if ever that is the choice you make (cause seriously, having a stoma, temporarily or permanently, may really bring the greater relief and allow you to live your life fully again). If ever he can't cope with it, then it's really unfortunate but to an extent, you don't want to be with someone that is shallow? That's always how I've seen things even though it's easier said than done. If he loves you for who you are he won't care!!!
I'll admit that what worried me the most was the dimension related to sexuality and the perception that would have my partners about it. Let's be honest: you can still be pretty, sexy and desirable even with an ostomy. Some guys may care but there for sure are plenty that will love you with or without it.
If ever you make that step, it's sure you'll have a transition period where you adapt to all the little details that are different, from taking care of the stoma to gaining confidence related to various situations (like going to the beach which, in my opinion, was the trickiest but totally manageable with one or two fashion tricks). You will sometime get mad as you learn but once that few months are behind, life is really good when it goes properly. You can generally eat like you never had before. You can enjoy the wonder of not having to rush for a bathroom and consequently have a better social life. Not having pain is also a great deal!
Anyway, in my opinion, it's really worthwhile to consider the surgery as an option and feel free to ask about any worries you have. By expressing them we will be able to help you reduce your concerns on these topics.