How do you tell your partner your sexuality has changed?

I have identified as bisexual for as long as I can remember having any sexual feelings. When I was fourteen I told several friends, I described myself as one of those rulers that snaps in the middle, I can be straight, I can be bent. Not the most elegant way to put it but it seemed to make sense at the time. No one ever really had a problem with it.

I had a few boyfriends when I was young, but I always fantasized about falling in love with a girl, and I’d get confused, so the boyfriends didn't last long. There were no other openly LGBT people in my school or community that I knew, so I didn't feel I had anyone to talk to about my feelings. I had my first girlfriend at the age of 19, she left me two years later to explore her own bisexuality, which was hard for me to understand at the time, as I believed in monogamy.

I have been in my current relationship with a woman for three and a half years, at first I think I experienced a bit of bi-erasure, without really realising it, I felt pushed into calling myself gay. It made sense; if you commit to someone in a lesbian relationship, should you not identify with that sexuality? In the end I thought there was no point in pushing the bisexual identity, she wouldn't understand, she’d think it meant I intended to leave her at some point. So I was gay and that was that.

However, for some time now, I've been feeling quite low, smothered, and anxious a lot of the time. I've not enjoyed spending quality time with my partner, we can go out and have fun, but I've not wanted to be romantic or have sex. I tried to pin point the exact moment I started having these feelings, I thought back to the past week to see if I was happy then, the past year, three years… I can’t remember the last time I felt truly happy.

And then it clicked, I don’t know what happened, I was just lying in bed one morning, and it was like a light bulb just turned on in my long darkened head. Everything was upside down and back to front. I suddenly remembered that I wasn't gay. But not only that, I realised that I wasn't attracted to women any more, at least not sexually.

In my adult life (I’m now 24), I have not had a serious relationship with a male, I always imagined myself as the type that could sleep with any gender, but could only fall in love with someone who identified as a female. I think a better term for this might be “homo-romantic bisexual”. So I thought I’d settle for a lesbian relationship. I have always had trust issues with men (repressed childhood father abandonment issues), and felt I could never find a man I would feel comfortable with. But I have found myself longing for a male companion more and more recently, I’m not sure if I could ever have romantic feelings for men, but I think sexually, I am now more attracted to men than to women. I don't know how or why this could have changed.

I’m now struggling to know what to do with myself. Am I a homo-romantic hetero-sexual? Sexually I need a man, emotionally I need a woman?

I think all of this is for me to figure out later. The first thing I need to know is: what do I tell my partner of 3.5 years? How do you tell someone you love that you don’t think you can ever be happy with them, that your identity clashes with their needs? That you love them but don't enjoy sex with them? I don’t think she’ll understand (she’s not very open minded about these things), and I’m terrified that she’ll say that’s it, and never talk to me again. What if I later realise that I can’t be with a man either and I’ve thrown it all away for nothing… I don't want to hurt her, but I don't know how much longer I can pretend everything is fine.

I thought I had myself all figured out, but now I feel like my magnetic pole has just flipped, I’m somebody completely different to who I thought I was. I feel like I'm going to have to come out again, but as "not gay", and this time no one will take it seriously.

I just felt like I needed to get this out. Perhaps someone has had a similar experience, or has some advice… Sorry it's long, and thanks for reading.