If working out by yourself makes you feel sad and lonesome, or if the only voice urging you to get up and exercise is your own and you’re ignoring the message, it could be that working out alone just isn’t for you.
Being physically active on a solo basis is perfectly acceptable, of course. As long as you stay motivated to keep it up. If you’re your own best workout buddy, go for it! For some people, being active is more fun and more motivating when it’s done with other people.