I (26m) feel uncomfortable discussing private life at work due to colleague's (28f) opinions

Tl;dr: A colleague at new workplace has narrow-minded views when it comes to sexuality. It makes me reluctant to bring up my relationship and in turn, I feel awkward and excluded during these types of conversations.
A little over two months ago, I started working for a small accounting firm. Four people are currently employed on a full-time basis, myself included. Our boss is the relaxed type and the atmosphere is friendly, which I view as a nice change compared to my previous call center job.
My colleagues form quite a tight-knit group and they socialize outside of work, too. Most of them are familiar with details of each other's private lives, which they'll often discuss over breaks. They've made attempts to include me in those conversations and I'd actually like to participate if I wasn't put off by one colleague in particular.
This employee has a very dominant personality, the kind that makes people gravitate toward her even when they disagree. That usually means that other colleagues are easily persuaded to take her side. I'm under the impression she sees herself as "edgy" by expressing controversial opinions.
One of these includes believing that bisexuality is a myth, i.e. a phase which you outgrow once you pick your team. Being a bi man myself, I felt incredibly awkward sitting there watching people agree with her as she explained her reasons. Apparently when it comes to men, it's because they can't like both "receiving and giving", which got a laugh from my colleagues. Meanwhile I was just looking for an excuse to leave before they could ask me for my input.
I've also noticed she likes to casually equate gay men with feminine stereotypes and lesbians with masculine traits in a joking context. Maybe I'm being overly sensitive, but these sorts of statements make me uncomfortable when the conversation turns to my private life. It's the main reason I've been dodging the topic of relationships. I have a long-term boyfriend (30m) and I'm not certain how my colleagues would react to learning that information. Then again, dancing around this subject makes me feel equally awkward and like something of an outcast during our hangouts.
My apologies if this sounds like a minor issue. I figured I should ask for advice since it's been giving me anxiety.
Do you think I should simply tell my colleagues? I don't think anyone at my office is militantly bigoted. Rather, they seem to talk this way because they believe our whole group to be straight. But that's precisely why I'm worried about their behavior after learning I'm not. Feeling excluded is no fun.


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