Dear LonelyDude,
I haven´t been online for quite a while and so I only read your question today. 
I am familiar with the feeling of being unwanted, undesirable and unattractive. My finacé has a very low sexdrive on top on his general attraction to men while I´m a woman. 
I´m happy to tell some more of why we are engaged anyway, but wanted to respond to your question on how to cope with these feelings. 
It was very hard for me. Still is sometimes. What helped me most was a confidante with similar experience. My financé is part of a group of men struggeling with their sexuality and actually it was him who connected me with the wife of another man. With her I could talk openly and she could relate by own experience. She allowed me to get in contact with her anytime I needed (even if I just wanted to scream from frustration). 
That woman is part of the reason why we´re still in this relationship. 
The other (not less significant) part is: I can talk about my feelings with my partner and he is willing to meet my needs. This quite often means me telling him explicitly what my needs are. 
Sometimes it's a balancing act between what I long for and what he can give me. But we´re willing to work through the difficulties, knowing how much we love and value one another. 

Please feel free to ask, if you have any questions. 
I´m wishing you all the best!

I just revisited this old post and stumbled across this sentence of @Dutchman again:

Dutchman wrote:

But what are his thoughts about sexual attraction as a result of love? Sure, usually it's the other way around, but who cares? Is there a law against approaching things (differently) than expected from mainstream?

About one and a half years later I´m still in the same relationship and I wanted to share some of my story. Maybe someone will find this helpful / hopeful. 

From falling in love and rushing in a relationship we have evolved into a very deep comitted partnership with heartfelt appreciation for the other person in their uniqueness. In a way the challenges and insecurities we both have to face are similar, although they might seem to be fundamentally different. 
Where my partner always struggled with issues of "being enough" and feeling accepted in general, I have had doubts wheter I could "be enough" as a woman to him.

Through countless talks and some rough times I discovered that within his SSA he is more on the asexual side of the spectre. Somehow this has relieved me. I feel less being in a competition with men he might be attracted to. His expression of not really being that much into the physical part of a relationship has in no way made anything easier on the practical part, but in my head. From there on the question was more, will he be interested in me and less will he be interested in me although I am a woman.
He always identified as being SSA and therefore this second question still is immanent, but somehow less for me. I guess that helped me being more relaxed in the whole process.

And this leads me back to the quote. My partner has indeed over time discovered a degree of sexual attraction to me as a result of love. From him not wanting any physical contact apart from holding hands, him being attracted to my mind, my voice, my personality (how wonderful and yet so frustrating when you long for being desired fo

Thanks again, Dutchman. 

I´m well aware of the pitfalls and since we´re striving for the things you mentioned in your post I guess we´ve got as good a chance at everything turning out right (or not) as any relationship that´s facing challenges. 
And since this whole relationship thing is new to both of us, we might as well discover that it might be easier than imagined. Or not. Who knows. But we´re willing to accept each other as we are, flaws and challenges included. It´s a progress of finding out what we both want individually and as a couple while being open about the challenges we´re facing and the joy we´re sharing. 

Concerning the aspect of religion: he decided not to have a relationship rather than one that went against his beliefs. Meanwhile he has put a lot of work in the self-acceptance part and got to a pretty good point. We´ve hat conversations about that and he´s definetly not trying to cover up or surpress his same-sex attraction by being in a relationship now. Suprisingly enough he wants to be in a relationship with me and has been very open and considerate towards me since the beginning of us dating.  
The thing that´s completely open as of now is the extend of his sexual attraction towards me. We´re moving slowly, taking a lot of time to discover what´s good and where we have to wait for the yet unknown outcome. So it´s a precess, sometimes testing my patience, yes. But when you´re in love, you´re in love. And love is patient

I´m glad I can share my situation here. As you can imagine, it´s not a topic you talk about with a lot of people.