I can't with my boyfriend...grr!!?

I have no problem reaching on my own...I usually use a vibrator, but I decided to try to reach one without the other day to "see if i still could" and BAM no problem. For some weird reason, I cant seem to reach with my boyfriend who I am totally infatuated with. Weve not been dating for 5 months, so its getting really frustrating. To top it off, he LOVES giving , and hes really good at it, but for some reason I just cant do it! I dont even get close, and he will go down for up to 25 minutes before I just get frustrated and stop him. Ive had s w/ other guys before. Whats going on, and how do i come w/ him??? I even pulled out the vibrator w/ him and even that didnt do it for me...help!