I can give you the perspective of one who has experienced a jealous partner, it's a very destructive emotion. It's exhausting to have to defend yourself, explain yourself when there's no cause for concern. It made me feel like I was not trusted or believed when I told him I loved him, it was incredibly distressing and exhausting.

Good for you that you recognise this and want to take action.

Some thoughts:

1) If your partner is going to leave you they will leave you, none of us can control another person. We all take that risk when we commit emotionally.

2) His friends add something special to his life, they help make him who he is, they likely support him in many different ways according to their own personalities. They enrich the life of man you love, in turn that helps support your relationship. No one person can be everything in another's life, that would be unrealistic, but you are his girlfriend and as such you are his number 1. Believe it.

3) If you haven't already, then maybe organise some group time together with his friends, get to know them a little. This may help you trust him and them more.

4) You don't really mention your own friends, do you also have people to spend time with? If you do then spending time with them will not only divert your attention into something positive, you will be investing in relationships other than your partner and that could take the pressure off. If you don't have too many friends then maybe look at widening your own social circle.