How to Break Up with Someone, Be SPECIFIC?

I'm going to go into detail because this particular guy has been challenging to deal with and I feel that ending our relationship will not be incredibly easy.

I (18) began talking to this guy (22) when in July. He just kinda slid into the DMs and I was never looking for a guy but I figured it was worth looking into. Early into the relationship I didn't really want to kiss, I just was shy. Eventually I did. However, later on I pushed myself to do more and I went to 3rd base with him. I soon regretted it and decided I didn't want to really do it anymore. He accepted it but couldn't understand. I wasn't super into this guy. I liked him but I'm a very distant person, which I told him, and I started to distance myself and seemed a lot less interested. He soon started to message my best friend via Facebook. Apparently he didn't want me to know that but he would message her to ask questions about me. At first this seemed nice but a little weird. Then he would contact my cousin the same way.

I like to visit my best friend at college and go out to a couple parties, nothing crazy. I'm not one for hooking up but it really bothers him, but he isn't my boyfriend. He bought me concert tickets for this band I like without telling me so we couldn't refund them. He asked me to be his girlfriend afterwards and I have never had a boyfriend before and I decided I wasn't ready. I continued being distant due to just personal reasons (depression, having a cold, etc) and he took it very personally and would throw all the things I requested him not to do in the first place in my face. He also pesters my sister constantly as well. We are kind of friends with benefits accept I don't really want to do anything sexual anymore. His attitude makes me not want to even be friends. He is very possessive and never believes anything I tell him. He thinks all my male friends are threats. He is not my boyfriend. All my friends and family have decided that he needs to go. How do I go about it? He always starts arguments.
How to Break Up with Someone, Be SPECIFIC?
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