Dear OB readers: How do you let a man know he doesn't satisfy you in bed?

From a female OB reader

What's the easiest way to let your man know you don't enjoy sex with him and you need him to improve without offending him? I have a high sexual libido and I doubt I will be faithful to any man who can't give it to me well. This is the man I intend to marry and I would really like to be faithful but my sexual satisfaction is very important to me. When he gives me head, he pretends to use his tongue when I know it's his fingers. He's also not big on foreplay and doesn't last long. He always leaves me unsatisfied after every sexual encounter. How do I let him understand without offending him? And can he even get better or is this how it will always be? Na only me waka come, make I know now so that only me go start to dey waka go