He's using me isn't he? What do I do?

I have a friend who is a guy: Ryan. I've been friends with him for 2 years, through put those years, he's had this on/off girlfriend: krissie. But 4 months ago, they broke up for good. He came crying to me about how heartbroken/ pissed off he was. I said: she's not worth it, you can do better, etc. Then, he told me he LIKED me! I'm thinking: "uh, I'm sure you just want another girlfriend or you want to make krissie jealous" he swore it was true ever since the day he's met me. I stupidly thought he was telling the truth and we went out for 2 months. Towards the end of our relationship, he told me (out of the blue) he wanted to lose his virginity. So I thought: 'why not?' and so we had sex. The day after, I was at his house and playing around with his phone. I scrolled through his contacts and saw: Krissie<33333 I was like: WTH?! so I told him about it and he said: oh my sister did that, I hate krissie, I really love you. I let it slide. That night, on facebook, (I'm friends with krissie on fb) her status was: 'I'm really missin' a certain some one and hope they miss me back ;) u know who u r by the wayy' Ryan's status was: 'hey I miss u and u know who u are too ;))' he doesn't know I'm friends with her!! Then he suddenly wanted to break up and he missed being just friends. and I was really pissed off! Guess who he got back with? 2 months later(which is now) he said: "I really miss you and I was so stupid for dumping you. Just saying, but maybe we could hang out at my place ;))" he's using me right? What do I tell him? I liked everything better when we were just friends. :/ Because I now feel like I'm just a back up plan whenever krissie dumps him.