Hello and Welcome to the Forum
It is good that you have found your way here for advice, but too be honest the best and kindest thing you can do for your guinea pig is to get him a friend.
There really is nothing else you can do that will make him as happy as having companion of his own species with him 24/7.
How old is he, and what cage is he in?
Is he an indoor or outdoor piggy?
If you can elaborate on the reasons you can't get another guinea pig right now then maybe people will be able to offer some ideas for the short term, but the reality is that it simply is not fair to never offer a guinea pig the opportunity to have a companion. Maybe this will be a possibility for you in the longer term?
A good place to start to learn more about guinea pigs in general is here:
Getting Started - New Owners' Most Helpful Guides