Playing with others is ESSENTIAL to becoming a competent-great bassist.
ACCEPT THE FOLLOWING:
STEP 1
1.You will make a fool of yourself.
I sang "Should I Stay or Should I Go" in my band when i was 14 at a neighborhood festival. It was awful. People laughed. It dogged me through high school. I would do it again (gulp) for what it made me become.
2. Nobody in the whole world thinks about you or your bass playing as much as you do.
3. You're going to make mistakes. Again. Again. And again.
4. You'll feel inferior in playing abilities to someone you play with.
STEP 2
1. Now when you go home after practice or jamming with someone you can work on the specific mistakes you made that day.
2. Competition breeds excellence. Is that guy really better than you? Can this never change? Opportunity to prove yourself wrong.
3. Playing with different people allows you to decide (actively or passively) what kind of bassist you want to be. Background? Trio? 2 Guitars one bass? Groove specialist? Prog Prophet? You're choice.
STEP 3 (the good part)
1. After playing with people for a while(hopefully playing with the same person or group for at least a few months), someone you know well will refer to you as "really good at bass". You'll be shocked and think it's just a complement at first, then after another time of hearing it you'll realize you've actually excelled.
a) You might also experience the awesome, awesome feeling of while noodling around on a bass or two at a guitar store, one of the good employees strikes up a conversation with you and starts putting the "private reserve" basses in your hands(Ya know, that $4,800 Custom Shop you've always wanted to try). He sees you're good and qualify to touch "the top shelf".
2. Your new version of "mistake" or "screwed up big time" will be 1/1000 of your previous definition.
3. You'll have confidence through competence and experience. It's music. It's art. You'll challenge yourself in ways you never thought you would and achieve more than you ever dreamed.
4. While playing a show and looking at the crowd with a grin on your face you tell yourself "I can't believe I was afraid of this".