My boyfriend has a low sex drive?

I’ve been with my boyfriend for a couple of months but I’ve known him for over 3 years. He’s a pretty great guy but I’m struggling with his low sex drive that he seems to have. My guess is that it’s low testosterone and/or stress. I want the best for him and I know that sex and romance is healthy for a relationship. I only see him about once a week. He’s 25 and the only guy I’ve met to not care for my advances or hints. He’s told me not to take it personally and I never force him to do anything he doesn’t want to but I can’t help but feel bummed out when he says he’s not in the mood. I plan on staying patient and understanding because that’s all I can do. I just wanted to know if anyone else has gone through this problem and if they have any advice for me.

Thanks.