Yes, your Network Admins are spying on you. The trade off is that if they do, you can't rely on the identity of any remote party you connect to via TLS; but if they don't, you might be taking advantage of the confidential channel to download malware, post proprietary documents to competitors or whatnot.
When I'm working for companies that use this type of filter, I take the filter for what it is: the IT department is assuming responsibility for the identities of remote parties I connect to. I therefore use https connections to work-related services as I normally would: if their filter gets it wrong and connects me to a fake CRM, for example, that's a decision that my IT department took on my behalf.
I avoid anything where I care about the identity of the remote end like online banking. I would never ask my sysadmin in real life whether she thought some random server was owned by my bank, I'm not going to start doing it via a proxy device either.