So basically one night when my friend went to sleep (we share a house) me and her boyfriend were sipping a few drinks in the kitchen just like normal friends do. I went back to my bedroom and he went back to my friend's room. A couple of minutes later he's texting me saying "if your not busy in the morning we can have some drinks" not wanting to sound rude I said "yeah why not?"
So he comes to my room jumps in my bed and we decide to watch a film. Throughout the film he had his arm around me and stuff but I didn't think nothing of it. After the film finished I switched my laptop off thinking he was going to go back to my friend's room but he didn't. So I let him stay in my bed (as a friend). To cut a long story short he started touching me and stroking me I really didn't know how to react to that so I told him to stop. A couple of minutes later he started touching me all over my body and then he started kissing my neck, he pulled me towards him and started kissing me we almost had sex but I stopped it. I feel really guilty every time I think about it I feel so sick I don't know what to do. I see him everyday and he's acting normal towards me. When we're alone he always put his arm around me or hugs me and holds my hand. I don't know what to do!

If you don't like him TELL HIM!! If your friend really likes him tell her he is cheating on her.. you risk her getting REALLY mad cause you let him kiss you. But it may help.. its good you didn't sleep with him! But its bad that he's still making moves on you. honesltly I would tell him to back the **** off that he is dating your friend. And you value her friendship (if you don't value the friendship then I guess it would b okay to b the "other girl") but it seems like you and this persons friendship if you share a house... so I would tell him straight up to back off threated to tell your friend if you do have to tell her.. expect her to b mad at first... as would anyone who just found out their friend almost slept with their boyfriend!

My dear, you can't let him continue with this behavior without firmly rejecting him and condemning what he is doing. That's what you should have done when he first came in your room alone.

When you allow bad behavior, you are assured to get more of it, so speak up, and tell him to cut it out.

That's what YOU do!! And no excuses. Tell his girlfriend!!

A few drinks doesn't excuse what happened.. but if you really feel bad about it tell him off and tell your friend or she'll be even more mad if she finds out later on and why would you let your friend be with a cheater? But if you want him you should tell him and he should leave your friend being the "other woman" doesn't ever go well.. plus is it worth losing a friend over..

It sounds like you don't like him - so why let him continue with this behaviour towards you? Unless you do like him.. You definitely need to tell him to STOP coming onto you.
Now.. as for whether you should tell your friend. You definitely need to tell her. Does he already have a history of cheating that you're aware of? If so, then you HAVE TO TELL HER. At this point, apart from letting him touch you for a bit, you can still come away as the victim and she might not get mad at you. But the longer this goes on, the increased chance there will be that YOU might actually do more than just let him touch you.
Your friend deserves the right to know what a scumbag she's with, and what she does with that information is up to her. Don't be surprised if she somehow turns everything around and blames you; some women automatically blame "the other woman" because that's the easy way out. Just stay calm, and explain your side of things. But you undoubtedly need to tell her.