awesome relationship terrible sex?!

I've been with the same guy for a very long time. He was my first but hasn't been my only, we've been separated a few times and that's when I've encountered different sexual partners. When we first started I thought it was great.... then when I did it the first time with someone else I realized I was missing out! Foreplay is like not even a thing for him and he doesn't go down! I've asked friends and they're response is guide him or tell him or show him what u like. I have 😑 it doesn't really work I think he's just bad at it! Which leaves me extremely horny and sexually frustrated. I've come close to cheating in the past but haven't.... then couldn't even believe I entertained that thought! But one of his friends has found himself in a sticky situation with two women. I know of both girls but r friends with one and she posted something on my facebook and outta nowhere I started getting messages from the other girl who I didn't know he had any relationship at all! So basically besides me and the parties involved I'm the only one who knows what's going on. I've confided in him about somethings about me. And I have promised to keep his secret a secret. I'm attracted to him.... I wouldn't want to do anything to jeopardize my relationship but a girl has needs!!! It's hard not to think about this person in THAT kinda way now 😑 I'm not looking for a relationship with anyone other then the person I'm with but some good sex once in a while would b nice!!!! I'm a terrible person for even thinking these things but what else am I supposed to do?!? Help!!