If you just wanted to be friends with him, then you'd do it.
You wouldn't give a damn what anybody thought about it and you wouldn't be here asking for our opinions.
Hon, stop trying to pull the wool over our eyes - and yours.
You like him. You can't have him the way you want. So you figure this way is the next best thing. So what? Why ask if it's "such a bad thing?"
Tasha, if you want him in your life because that's what makes you happy or that's what you need right now, then do it.
When you're finally ready to let go, then the relationship will gradually fade away and you'll move on.
If he grows up and gets a clue before that happens, then your gamble will have worked.
If not, you'll have given yourself a brief interlude of enjoyment.
No harm, no foul.
Now, stop obsessing over your relationship with this guy and let us answer questions on some other subject. Got anything different you want to ask?