Looking for advice.

This is my very first relationship and it will be three years in a few months. We broke up two or three months ago (because he thought our sex life was dry and he didn't want that). After the break up, we kept in contact (texted every day) but it was odd in the sense that we would be platonic but also romantic/flirty with each other. We got back together a month afterwards because after I said I was starting to move on and wanted to get back out there, he started getting jealous and asked to get back together. I was wary at first because I didn't want it to be fueled by jealousy. But we did end up getting back together. 

The first month went well. Then we got into an argument. He invited me to stay over (he works often and I got to college so we rarely hang out except for literally only one day out of the entire week). We were chilling at his house until he asked if I want to go out to eat dinner with his friend (female). I said sure but then his friend texted asking if it was okay if it was just him because she wanted to tell him some personal things. To clarify, this would mean he would be leaving me alone at his house. I was like "uh sure?" I didn't want to get in the way of his friendships but I didn't like that he chose to spend time with someone else on "our" day (he left at 7PM, came back at 1AM). Anyways, it wasn't a big deal until the next night where he went out with the same girl LITERALLY the next night (just to emphasize). So I was like what the hell dude why did you HAVE to hang out with her the day before then what the fuck. So I got pretty salty because I didn't think that was right. We argued, he called me a waste of time. I got hurt because like why would you say something like that wtf (he said he didn't mean it and it was just to spite me like ok). I ignored him for two days. I was mad. I needed space. (He didn't apologize either until I asked him about it). 

During the two days we didn't talk, he said he went to thinking and said he didn't know if he wanted to be with me anymore. I'm like uh what do you mean. He said "I don't know what I want in life. That includes school work etc and you. I want to open our relationship". Personally I'm against open relationships because it's like allowing someone to cheat on you but that is my own opinion. I was against it so I said why don't we break up so you can explore (during our initial break up he went on tinder and talked to some girls too). He said "but I don't want to break up". 

????? I don't know what to do. To this day he keeps saying he doesn't know what he wants but he doesn't want to break up because he loves me but he doesn't know if he wants me. I'm confused as fuck. I feel like I shouldn't be wasting my time and effort with someone like this but at the same time I don't want to throw away an almost 3 year relationship but I mean I'm only 18. He's acting like everything is normal and that bothers me the most because he is second guessing us and possibly wants to meet/is already talking to other girls. I don't know how I feel about that. I asked him and he said he wasn't talking to anyone. He asked me to be patient and understanding which I initially suggested at first before him suggesting an open relationship. But how can I act like everything is okay when I'm always stressing over whether he met another girl yet or if he's trying to meet other girls. What do I do. 

Sorry for the long post and annoying teenage feels shit. Please guide me because I'm lost.