I’m losing interest in engaging sex with my girlfriend

So me \[35M\] have been dating my girlfriend \[33F\] for about a year and a half now, and have been living together for 3 months. We get along well for the most part, except when we get into small arguments due to her temper and being over-sensitive in some situations. Basically she can have a quick temper when she hears something that she doesn’t like or can get kinda defensive on certain things. Let’s just say some of her habits are not pretty but I accept that not everyone is perfect. On the positive note, she is a kind-hearted and loving person to be with, and genuinely cares for my well-being. We feel comfortable with being around each other living our day to day lives.

Now to the more important issue here. Sex with my girlfriend have never really been that fulfilling, and it almost feels like a chore to do it with her as time goes on. I’m not excited nor do I enjoy the process. I’m not sure why and feel conflicted. She has never experienced an orgasm nor does she experiment with her own body that much, and I also have a problem climaxing when having sex with her. I genuinely feel like I’m not sexually attracted to her anymore and I’m trying to find out the causes of this. I always get the blame because of how I’m not able to finish during sex, since she will eventually want kids in the future. But she does offer words of support and encouragement even though I can feel her frustration. I brought up the solution that we can both exercise more and eat healthier and hopefully that will improve our sex life, but she argues that it is irrelevant and wants me to see a doctor or sexual therapist. We’re both average sized and have been somewhat out of shape due to lifestyle choices and being unmotivated to workout more.

Could it be as simple as that’s just because how male biology works? Is it because we are “sexually imcompatible”? Could it be as simple as a person’s scent? Could it be because I get turned off by her temper or certain habits that bugs me? Could it be something like her always trying to look at what I do on my phone and who I’m texting? Could it be her making loud sneezing noises every morning when I’m still sleeping? Is it because we don’t share enough common interests and hobbies? Is it because we’re not exercising or eating as healthy as we should be? Will improving on exercising and dieting fix our sex life? Could it be because I use to watch porn regularly before but now making a change to not masturbate to porn anymore? Or is this something way more internal at a core level?

I really want to get an insight if anyone have ever experienced this. I want to narrow the causes and try to focus on working on them. Any tips and advice will be greatly appreciated!