@won-der-ing,
Thanks for the further info, won-der-ing.
It's hard to know what to advise. As a parent, I'd want my kid to feel able to talk to me about anything at any time. And I'd tend to think most parents would want to know this kind of thing (I don't mean the sex issue per se but the more general stuff you're talking about, how you feel misunderstood and you cut yourself off from the family).
But it's possible you really would be shot down... I'd hope not, but I can't make any promises from here.
Maybe you can get your mom alone sometime and kind of slowly build up to things. Talk about much more general things and then slide in some of your concerns in a gradual way. See how she takes it, go from there.
I will say though that this background makes me even more nervous about you having sex with your boyfriend. I'm glad he's there for you and that he's so considerate, but I think that sex can be a proxy for other issues with intimacy. And it sounds like you are just not getting the love and support you need from your family. It can be really dangerous to put all of your eggs in a basket as fragile as a single romantic relationship, as a 14-year-old. And sex just makes everything much more intense and the stakes that much higher.