Me and one of my closest guy friends have been knowning each other for about a year now, and we have been friends with benefits for as long as I can remember, (and no he's not using me and I'm not using him because we put our friendship first over everything... we have strong trust, feel comfortable to be 100% ourselves around each other, and tell/do things we wouldn't do in front of most othr ppl) he's sometimes an a-hole/acts like he dislikes me/acts like ad***but that's just his personality. But currently he's talking to this girl he got with about a month back and I don't think she's good for him,(She doesn't know what we do/talk about etc) Even his parents agree to that and think me and him would be perfect for each other along with most people at our school. But he gets uncomfortable and acts like he doesn't want that to happen. The topic was brought up a few times about taking what we have to the next step, but the answers he keeps giving are in a nutshell him basically questioning himself if he made the right choice. And the thing is, he told me he's not even sure if he likes her, he's just dating her because she's cool. I'm really trying to understand his true feelings for me at this point but its just so confusing at times, please help :/

So many people (mostly girls and women) come here talking of a wonderful relationship, but as they peel the onion, the tears flow.
You start all happy with your FWB for a year now, but now that he is fooling around with another girl, you suddenly aren't so sure about FWB. Of course not - it rarely works out. He has his cake and now his cupcake too. Stop sleeping with him. You don't get to deliver any ultimatums, but you do get to break it off. If he cares about you enough, he will realize immediately that he can't play the field and have you too.
That would bring your relationship out of FWB and into regular BF and GF.

You are his friend with benefits and he wants a girlfriend. It bothers you because he is dating another girl and you will no longer be the only one. Stop having sex with him and see how serious the friendship is. How old are you two?

You really don't get this? You've had casual sex with this guy for as long as you can remember. There is no more importance to doing that, than saying you've been playing basketball with this guy for as long as you can remember.

Why on earth would he want more from you. He has it all. Friendship, and sex. No ties, no commitments, nothing more than a 'simple' friendship, which leaves him (and you) in a position where either of you can get a girlfriend/boyfriend, and suddenly become mature enough to want more than sex in a relationship.

You aren't it.

There are consequences to everything you do in this life, and you are facing the consequence of how your friendship is not going to change what the friendship could have become, or might become, had you not decided to degrade yourself the way you have.

Casual sex is just that. Casual. No strings, no expectations. Of no importance, other than the sex itself, which, should be reserved for a more serious, mature, actual relationship.

If you can't see that much of an explanation into your 'friendship', you surely won't have a clue as to why he's seeking something more.