It doesn’t fit... seriously

I met a guy and we don’t really have a *spark* but it’s amazing when we hook up. The first time we hung out we tried to have sex but he couldn’t fit, which we both attributed to nervousness. But then we tried again on another occasion (in multiple positions) and he still would not fit without a lot of pain. He is on the larger side, but plenty of girls can take bigger guys no problem. I did some reading online that said I need to “stretch” myself out but I’m not sure how to go about doing this being that I’ve had sex with other guys that were smaller with no issue. He’s being really sweet about it but it is embarrassing. Has anyone else experienced this?