Why is it so difficult!!

So me and my boyfriend have started having sex for the past couple of months and each time he finishes and I don’t. I don’t have a problem with this because I know even though I can really be enjoying it I just don’t feel the urge to so we stop after he’s finished. So last night he wanted to focus on me which I mean I wasn’t exactly complaining but even though I was extremely enjoying it I felt more uncomfortable than feeling like I was going to finish and ended up bleeding so we had to stop. He told me that I’m extremely difficult to get to cum but said we can try again and made me feel really happy because he didn’t make me feel bad about it not working. Now I’ve tried doing it myself but I can never get the same feeling from when he’s doing it so I’m just wondering is there any tips on how to make it easier? I know it’s different for everyone but anything really would help! Thank you!