How can i relax, and not get jealous?

There is this guy that i met about a month ago. Hes such an awesome guy, and so funny. We take our breaks together all the time, and joke around. When i first met him, i thought he was cool, but his ex was just moving out, and i was still technically with my now ex. Well, almost a week ago, my roomates and i had a small kickback. One of my roomates ended up leaving with her friend, so it just left me and the guy i like. He started playing songs for me on his guitar, then we went to my car to grab something i had for him. He was like "well i guess i owe you, right?" and kissed me out of nowhere. We went back in the garage, and i was resting my hand on him. (i should have pointed out that we were both drunk) So he says"are you trying to touch my weiner?" so i said, no if i was i would be doing this. and rubbed him. So we start making out and im touching him, and give him a bj. Then we realized it was 7 in the morning and he had to go pick up his son, so he said to put his guitar in my room so its proof that he is coming back. I asked him the other day, and he said i should just bring it to work one day. And he mentioned that he wants 3 months of being alone. which i completly understand after that big of a breakup. He still acts the same around me, except he will openly flirt with other girls around me. Normally, i wouldnt care since we arent dating or anything, but it still kinda hurts. And i know its not smart, but everytime he bails on hanging out, i ask my ex if he wants to hang out and we end up having sex. (he broke up with me for our age difference). I just want to be happy, and let everything just fall in place, but i dont know how.