Boyfriend and I didn’t have sex.

I’m not sure if I’m overthinking but my boyfriend and I have been arguing and haven’t seen each other in 3 weeks . Last night we went to dinner and drinks then went back to his place and he just like wouldn’t get hard and I mean it’s happened before. I got mad because we haven’t had sex in 3 weeks so I’m thinking he’s been sleeping with someone else because he didn’t want to have sex with me . It made me feel really unwanted and rejected. I don’t mean to sound conceited or anything but I’m an attractive girl and I’ve never had to feel undesired especially sexually. Did I overreact or was I right for getting upset with him?