I get jealous when my boyfriend spends time with other people? Please help, don't know what to do?

My boyfriend and I have been together for 9 and a half months now, really both of our first serious relationships. We have a very intense relationship and we have had some issues because I have some mental illness which has often strained the relationship. However we do not intend on splitting at all and we have discussed one day getting married etc. The problem is that he has many more friends than me, just because I am generally very shy with new people and so I never really immersed myself in a large group. I also don't have close relationships with my circle of friends because we are not the type of people to be close if you understand. Therefore, my boyfriend is really the only person I am extremely close to, and it's lovely because we can talk about anything. It's just that he is very close to his family and extended family, and his friends, and so I feel like I am much more dependent on him than he is on me. I know he loves me to bits, but I just can't help being insanely jealous when he spends time with other people, family, friends etc. I am aware it's immature, but it's eating me up inside completely. Without him talking to me online, or being with him I feel intense loneliness and when I find out he can't talk to me because he is spending time with his family, or he is at a friends house I act like it's fine but really I get upset and angry and it brings me down for the entire day. Sometimes I feel like ending the relationship because as much as I love him and Love being with him, when I don't have him to myself it hurts so much that I begin to wonder if it's worth it etc. Which I know is ridiculous. We only get to see each other for 2 days a week because we live too far away and studies get in the way, soon he will be going to uni. He isn't going far away at all, just an extra 40 minutes on a train, so about a 2 hour journey, and so we will still take it in turns to visit each weekend and spend the same amount of time together, and then the year after I plan to go to a uni very close by so I know it will be great when that time comes, but I still feel sick whenever I think of him making new friends etc. because I feel left behind. he is an amazing guy, he would never cheat and I know he thinks the world of me and constantly tells me how lucky he feels and how he doesn't understand how he got me and stuff, but I just don't see it, I feel like some kind of parasite, because I need him, and I feel like he can cope so much better without me than I can without him. I don';t know what to do, how can I stop this? I have low self esteem and depression etc which I know is part of it, but I just can't shake the feeling that it hurts to love someone this much, and whether it is worth it?
I get jealous when my boyfriend spends time with other people? Please help, don't know what to do?
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