Okay. You're saying you love your girlfriend - yet you're considering breaking up with her, and I'm not even sure over what. At the end of the day, there's nothing wrong with being gay or bi.
My cousin is 20 and she's had two girlfriends, and recently proposed to her current girlfriend. She loves kids, she works in social care. And frankly, I think they'll end up finding some way of having their own family. So having a girlfriend is not really an important factor in having a family, because there are ways of doing so.
If you're seriously considering breaking up with her, I would say you don't love her as much as you're saying. To be ashamed of being a lesbian and adopting is silly (and donor pregnancies are also possible and not uncommon for same-sex relationships).
Why really worry about being judged and what other people think? If you love someone it shouldn't matter, and people are more accepting of same-sex relationships now than ever-before. It is 'social norm' to be gay/bi in most life situations.
You need to think about whether you want to split up with your girlfriend because you don't love her anymore and want to have a relationship with someone else (male or female), or whether you're over-analysing everything and being silly. If you make the wrong decision you may lose the person you say you love. I feel like you're just insecure about being bi/gay when it isn't even a big deal. People don't need to know that as the first thing about you, concentrate on making friends and enjoying yourself. The fact you're in a relationship with a girl is irrelevant to everything (really).