I can’t get hard when having sex with my fiancé

Hey everyone, so I been having this issue with my fiancé (which I’m surprised she still wanted to get married despite the bad sex on my part) but I’m having a really hard time getting in the mood and wanting to have sex with her and I feel super guilty about it. She believes I’m really unattached to her but wouldn’t say that. I’ve been with her for almost 4 years and we’re havjng sex like once a month now. She mentioned that she needs sex and that’s a low amount to have in a month but that’s all I can physically give her. I’m not sure if I’m in my head because I’m in an interracial relationship and not used to it or what the issue is. I also feel guilty that she loves me way more and I don’t feel the extreme love she feels for me. Any suggestions?