I can relate to your thread very much and thought I would come and join it.
I don't want to project my experiences onto you. I can only share my experience, as it is very similar to yours.
I was also with a man for around 5 years. My longest, deepest, sweetest relationship. He is definitely someone I'd consider a soulmate. I can't even begin to describe how attached I was, and still am, attached to him. But the passion was just not there. I found him gorgeous to look at - I still do - and I am sometimes even now still a little attracted to him. But the idea of sex with him, or any man, just doesn't set off that same 'zing' as women do for me.
I met a girl whilst I was with this boyfriend. I was still deeply in love with him at this point, but our sex life was barely existent. And, yes, there was little excitement any more. To my amazement, when I told him that I found her attractive, he suggested that I start seeing her, whilst staying with him.
After 6 months, I felt about her the way you seem to feel about your girlfriend. The sex was out of this world mind-blowing. It was fun, cute, passionate, exciting - all of the things you are describing. I felt like I wanted to live with her, spend my life with her. She made me over-the-moon happy.
But I couldn't bare to leave him. We had the deepest bond, deeper and more spiritual than my bond with her.
Here's where the tricky part comes in.
Poly can work because
you find different things in other people. If I could have had him and her at the same time, I would have been happy. But this wasn't working for him any more. So I ended up choosing her and I haven't dated a man since (we broke up about 4 years ago).
When we broke up, I told him that I needed to explore my attraction to women. At that time, I thought we would someday get back together. I just couldn't imagine living without him. And I still can't - but I don't think either of us would go back to that kind of relationship, after this good space and exploration time.
It is very possible that you are primarily into women. I feel that way, at this stage in my life. I feel like I have found my sexuality - I simply prefer women, in sex, in love. I still find men attractive and would consider sleeping with one - but it just doesn't have that same pow factor.
Now, in my situation, I am still very close to my ex boyfriend. In fact, I'm currently living with him, sleeping in the same bed in an open plan studio, but dating women. We aren't romantically involved any more. We are just.... very, very close friends... platonic partners. We take holidays together and sleep in the same bed, we walk around naked in front of each other, I give him a hug or a kiss before work every day. A lot of people think that has to be romantic. I don't.
If I could live in a big house with him and my current girlfriend, I would. And for us, it would actually work.
If your heart is not in the relationship with your boyfriend any more, you have to confront those feelings. I was so scared to let go of my relationship with my boyfriend. It was one of the most painful things ever. But at least now, we can still love each other without hurt or unmet expectations. And it gives him the emotional freedom to find someone who can love him with passion. Think about the way you see your girlfriend - wouldn't you love him to have a girl that feels that way about him? Whilst still being platonically very close with you?
Incidentally, the great relationship with the girl I left him for turned very sour after less than three years. It went from beautiful to just plain annoying. But having that time away from him helped me discover what I wanted. Now I'm in a relationship with a new woman, who I've been with for just over a year. When I was with my ex boyfriend and girlfriend, I used to think that you could only find one thing at a time in relationships - passion or soulmate kind of love. I truly didn't believe the two could cross over. Now I'm with a woman who I feel that deep spiritual love for - AND the passion is intense. As well as the fights
If I'd never broken up with him and seen where things went with my ex girlfriend, I would never have experienced the kind of love I have right now.
So, I think that you need to do some thinking.... and some talking with your boyfriend... it sounds like he does need more from your relationship and that his feelings are stronger than yours from a romantic perspective. Are you at a time where you need to explore? How old are you, incidentally?
And if your relationship is special, it might be that over time, you don't have to give each other up, but that your dynamic could just change.
I started asking myself questions. When I watch movies, do I look at the women or the men in sex scenes? Have I ever even had a crush on a famous man? If a man and woman were naked in front of me, who would I want to have sex with, deep down?
For me, it kept coming back to women.
Only you know where your sexuality stands. I definitely think you should talk to him and at the very least, discuss a trial separation of six months, where he should try to date other people and you pursue your relationship with your girlfriend. I actually think that almost every relationship I've had has ended with a soft "we'll see where we stand in 6 months".... then 6 months comes along and suddenly everything's clearer.