I'm sick and tired to feel unreasonably undesirable. My gf is sweet and always kind to me, and it'll calm me down but only for a while. But then something will trigger me all over again. This time, she simply just said to me she would feel bad not having sex ever again in her life. She knows I'm asexual. 

I can have sex to please her, but I have a lot of discomfort and feel easily angry, restless or even suicidal when I cannot relax or enjoy sex like everyone else do. I'm afraid that if I decide to be less..."sexually active" with her, she will eventually leave me. I could open the relationship, but I'd be way too jealous and unstable at the thought of her having an intimate moment with another person. I know logically she wouldn't leave me (???), but the fact that I cannot meet one of her basic needs in a consistent way make me anxious. I mean, I could do it consistently, but my mental health will have to pay the price. But why do I worry about that....my mental health will be shitty no matter what....

On top of that, I feel guilty to be like this. She could have a better boyfriend, but no, she's stuck with me.  I'm not even that affectionate or cuddly. I'm nothing good as a partner, there's nothing good about me. I shouldn't be in a relationship at all.

I also get paranoiac that maybe she only loves me in a sexual way than in a "humane" way. 

God, this is so tiring, I never feel fine no matter what. I hate how I am.