Sex life help.

Sooo I’m my boyfriends first everything. Kiss, sexual partner and even girlfriend. I’ve obviously dated guys before because I have a 3 year old. I’ve never had a problem making a guy cum ever but, I just can’t get him to cum. I do everything from going down on him and even riding him. I just can’t get the job done. He’s on antidepressants which can delay sexual drive. I just feel like there is something wrong with me. Even though he reassured me I’m doing a great job. I’m not really sure what to do.