How can I maintain my motivation to stay fit after having 6 weeks off?

If you were feeling so much better and it kept you motivated then I don't think you're going to have much of a problem going back. In fact I think it's going to be hard for you to stay away. If you're really worried ask the gym owner if you can just hang out or even wipe down machines(yucky job I know) but it will keep you in the gym atmosphere and want to get back. As for for-injuring yourself You need to talk to your surgeon and other doctors for their advice. Show them how you were lifting and tell them how much you were pushing yourself(be honest). They'll tell you exactly what you need to know so you won't have to worry. Have a speedy recovery!